Instrument air is required on the plant for control purposes. Further equipment requiring air are the silo filters and silo vibrators( although these can also be electrically actuated). Two screw compressors are employed for this purpose with a duty / stand-by configuration. Screw compressors are chosen for this application due to their small footprint. The compressors are fitted with integral desiccant dryers that are designed to ensure that the dew point is such that moisture does not form in the equipment. A specially designed header pipe can be used for air storage instead of a purpose-built pressure vessel in order to optimise plant footprint.
The plant is delivered together with an electrical container which is insulated and split into three compartments. The first compartment houses the HVAC equipment, the second the MCC, and the final compartment is used as either a marshalling room or for the PLC / DCS. Air conditioners are also installed in the container prior to shipment; thus, minimal work is required on site. The MCC is contains a UPS, low voltage lighting circuit and the variable frequency drives.
The intermodal containers can be insulated for harsh environmental conditions and the geometry of the containers lends itself well to this. The containers are fitted with ventilation systems to ensure sufficient air changes take place to provide a safe working environment for personnel.
As the containers are modified and fitted out at the preferred point of manufacture, to enable protection for shipment, false walls are fitted which can be easily removed prior to installation. Once on site the panels are removed and the individual containers are coupled up and weatherproofed. Additionally, to minimise site labour during installation, selected electrical cables are preinstalled, rolled back prior to transport and are easily reconnected on site.
All container external structures are designed to be simple bolt-on, with the weight of the container being used to fix structures in place.
The control hierarchy is critical for correct polymer dosing. The polymer demand by the downstream operation is linked to the polymer make-up and dosing facility. The water to powder ratio is critical for the polymer usage at the end user, this is achieved by measuring the make-up water demand and adding the correct amount of polymer powder via the VFD controlled Aerowet™ units. Interlinking of two or more hydration units requires steady control. A 65 % turn down capacity is achievable for this system.
Fabrication and site build period
Standard processing equipment and units are employed, thus negating the use of specially designed equipment which leads to a reduced fabrication period. The site assembly and commissioning time is short as all equipment has been assembled and pretested in the construction yard. This minimises the construction and commissioning crews that are required on site. Typically, when construction occurs on site the civil foundations need to be laid before other construction activities can commence. Using modularised systems allows for the plant to be fabricated at the same time as civil foundations are being poured and thus reduces this delay.
The use of sealed containers to transport the plant to site reduces the amount of losses that are experienced during transportation. All equipment meets normal transportation envelopes with only the silos being break bulk.
Conclusions n Shipping times can be greatly reduced with equipment remaining within shipping scales. n Footprint and civil requirements are generally lower when compared with a batch hydration system. n Site build period can be greatly reduced due to offsite testing and no civil foundations required. n Typical cost savings on fabrication materials alone can be > 20 % when compared with conventional batch polymer equipment. IM
* Jamiel Muhor, BASF Australia Ltd, Ronald Michalczyk, BASF Corporation, Mark Marcus and Tanya Marcus, ProProcess