Environment industries archive
Key departmental publications, e.g. annual reports, budget papers and program guidelines are available in our online archive.
Much of the material listed on these archived web pages has been superseded, or served a particular purpose at a particular time. It may contain references to activities or policies that have no current application. Many archived documents may link to web pages that have moved or no longer exist, or may refer to other documents that are no longer available.
|VHSP Pty Ltd built its tanning plant in 1987 using the Sirolime process, which delivered significant improvements in environmental performance over conventional processes. The company implemented further cleaner production initiatives relating to recycling of chrome tanning liquors that achieved annual savings of $314,000 with a payback of 0.4 years.|
VHSP Pty Ltd undertakes chrome tanning of cattle hides. Approximately 85 per cent of hides are received as green hides from abattoirs, with the remainder being salt-preserved hides. The VHSP tanning plant was built in the late 1980s using the Sirolime process developed by CSIRO.
The hides are ‘fleshed’ to remove adhering fat and flesh, which would otherwise compromise the tanning process. These fleshings are sent to a rendering plant to produce tallow for soap manufacture. The hides are tanned in large rotating drums. The tanned hides, known as wet-blue hides, are then passed through rollers (sammyer machine) to remove excess tanning liquor before packing for export.
Tanning is undertaken to stabilise a protein in the skin (collagen) and hence stop the skin from degrading. The tanning operation traditionally produces effluent which is high in total dissolved solids (TDS), suspended solids (SS) and biochemical oxygen demand (BOD), plus salt, chrome, nitrogen, ammonia and sulphur compounds.
Conventional wet-blue tanning involves four operations which are undertaken in large rotating drums.
These stages are:
The VHSP plant was built using the Sirolime technology, which delivers environmental benefits over the more traditional process.
Elements of the Sirolime process include:
The major benefit of the Sirolime process over the conventional process is a reduction effluent volume and improved effluent quality. The typical reductions that can be from the Sirolime process are detailed in the following table.
Chrome Liquor Recovery
VHSP has further modified its process to improve chrome liquor recovery. Chrome liquors contaminated by grease, fats and suspended solids could not be recycled as part of the Sirolime process, and included liquors discharged on the floor when drums were emptied and liquor squeezed from hides in the sammyer machine. These liquors, which represented 55 per cent of the total chrome liquors, were discharged to the on-site treatment plant.
VHSP developed a system where fats and solids are removed from the waste streams using hydrocyclone technology (refer to the flow diagram). As a result, the recycling rate for chrome liquors has increased from approximately 40 per cent to above 95 per cent. The recovered fat is sold as a high energy stock feed additive.
The original system requires the use of special trailers to collect the hides and chrome wash liquors at the end of the tanning cycle. Chrome wash liquors are pumped from the trailer to the hydrocyclone system.
The costs and benefits from the system are detailed in the following table.
|Reduction in trade waste charges||$171,540|
|Reduction in chrome sludge||$32,760|
|Reduced chrome usage||$60,000|
|Sale of fat||$60,000|
|Total Annual Savings||$314,300|
|Payback Period||0.4 years|
The environmental benefits have been similarly significant. The reduction in total dissolved solids, which is mostly salt, is particularly relevant to any similar operation being undertaken in rural Australia.
Estimated Reduction Achieved (tonnes per annum)
|Total Oxidised Sulphur||149.6||37.9|
|Chrome III||50.0||not determined|
Wet-blue tanning typically uses up to 30 litres of water per kilogram of hide produced. VHSP has reduced water usage to approximately 6 litres per kg of hide produced.
The Sirolime process was chosen for the plant in 1987, as an essential strategy for obtaining the necessary development approvals. Reduction in operating costs has been the main driving force for the further recovery of chrome liquors and fats using the hydrocyclone system.
Unloading the tanning drums
The main barrier to development and implementation of the system has been competing demands for limited resources within the company. The potential for the chrome liquor recovery project was first identified several years before being implemented in 1996. The resource barrier was overcome by the employment of university students during the summer vacation period.
Variable speed drives (VSD) on drum drive motors
VHSP has implemented a plan to replace all the original three-speed electrical motors for rotating tanning drums with single speed motors fitted with variable speed drives (VSD). The installation of VSDs has two main advantages: increasing torque, resulting in improved drainage of process liquors within the tanning drums, and a reduction in the consumption of electricity used for rotating the drums.
Hides in the tanning drums are constantly tumbling within the drum during processing. This causes an uphill and downhill effect with respect to the load placed on the motor used to rotate the tanning drums. During the tanning process, the drum is half filled with process liquors and hides and at the end of each stage the liquors are drained to tanks. As the drum drains, the weight distribution within the drum becomes uneven. Extra torque is required by the motor to continue drum rotation.
Original three-speed motors have set speeds and torque settings. They are unable to continue rotating if all the processor liquids are drained and the weight distribution within the drum becomes too uneven. Single speed motors fitted with a VSD can have their speed settings varied and resulting additional torque can be utilised to drain the tanning drums completely of process liquors. This achieves an improved capacity to recycle process liquors, less carry-over of liquors from different stages of the tanning process, and a reduction in the amount of effluent that requires treatment in the effluent plant and disposal to sewer. Previous to motors being fitted with VSD, drums were not completely drained. At the end of the process, wet-blue hides were unloaded into trailers along with 20% of the chrome liquor from the tanning stage, and the liquor from the trailers was pumped to the hydrocyclone system. This operation was inefficient and problematic requiring additional manual handling, pumps and a pit system.
The utilisation of electrical energy is optimised using motors with VSD. Three speed electrical motors have only three speeds available to rotate the tanning drums. These speeds are not always at an efficient level for a particular stage of the process, and with only three settings the difference in electricity consumption between each setting is considerable.. However, VSD - controlled single speed motors can provide a large number of speed settings, so that an efficient speed setting can be utilised and only the required amount of electrical energy is consumed to rotate the drums at a particular stage in the tanning process.