Fieldbus Technology: Success Story In Water Treatment Plant

The new Fieldbus Technology has proved to be very fast since the data available is in the digital form and hence the time required by the controller to process the data is less, explains Geeta P. Makhijani

Rashtriya Chemicals & Fertilizers Ltd. is a Government of India Undertaking and one of the leading manufacturer of fertilizer brands such as Ujwala and Sufala with production of 300MTPD at the plant at Trombay. The plant was commissioned in the late 70’s and has been upgraded on a regular basis to meet the high quality standards of the manufacturing processes.
RCF implemented Foundation Fieldbus Technology in the Sewage Treatment Plant named as “Sujala”.
It was a novel scheme, which reclaimed sewage from Mumbai Municipal Corporation, which was being disposed off to the sea. Tertiary treatment followed by the state-ofthe- art Reverse Osmosis technology was utilized to produce potable quality water.
This was the first plant of its kind in Maharashtra and the largest in India. The objective of“Sujala” was to ensure uninterrupted supply of water to the process plants at the Trombay complex.
“Sujala” achieved savings of 3 MGD water for use of citizens of Mumbai (as sewage was reclaimed and used in process plant, thereby reducing load on BMC) and reduction in blow down from process plants due to better quality of water.
The Fig. 1 shows the block diagram representation of the sewage treatment plant. The plant is divided into three sections viz. Primary, Secondary and Tertiary. The primary process takes the raw sewage and the latter is aerated and the bacteria are allowed to settle down. The secondary process ensures the separation of sediments from the water by using the Two-Stage Clarifier and addition of Polyelectrolyte resulting in the formation of beds. The final stage is the reverse osmosis where the high degree filtration of the water takes place resulting in potable water of the same quality as that supplied by BMC.
Foundation Fieldbus based instruments are installed in RGSF (Rapid Gravity Sand Filter) section.
There are six DP Transmitters, which are based on Foundation Fieldbus based technology. It was new and for the first time installed in RCF in 1998. The DP Transmitter measures the differential pressure across the RGSF bed. The DCS System was based on Foundation Fieldbus Technology and based on open architecture based on Windows NT platform. The Foundation Fieldbus devices communicated onall digital bi-directional serial communication system that interconnects the devices in the field to control systems. Being a digital system, the precision of the data carried was more than ever before. Foundation Fieldbus communicated the information at high speed due to the ability to distribute the control among intelligent field devices.
There were significant benefits that were realised from the application of Fieldbus Technology. The benefits were as under:

Hardware Reduction:
The Foundation Fieldbus used standard“Function Blocks” to implement the control strategy. Many function blocks like AI, AO and PID, could be performed by the field devices through the use of function blocks. The distribution of control into the field devices reduced the amounts of I/Os and control equipment needed including cards, cabinets and power supplies.

Installation:
The Fieldbus allows many devices to be connected to a single wire pair. This resulted in less wire, fewer intrinsic safety barriers and fewer marshalling....

cont....

To Read Further Subscribe Your PRINT COPY Today.