Sugar Industry clinches unique boiler design by CS Holdings in R38 million project

System Integration & Control Systems Design

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May 2000 System Integration & Control Systems Design

CS System Solutions

South Africa's sugar industry has seen the first watertube fitted with a controlled superheater, utilising an integral 'sweetwater' condenser to provide spray water, installed, commissioned and tested at Transvaal Suiker Beperk (TSB)'s Malelane sugar mill. The R38 million turnkey project comprising a dual-fired watertube boiler, civil works, boilerhouse, electrics, instrumentation and gas clean-up equipment was awarded to industrial boilermaker John Thompson Africa in April 1998. The design, supply and installation of all instruments and electrics, programmable logic controller (PLC), scada and software engineering were subcontracted to CS System Solutions, a division of JSE-listed CS Holdings.

The design criteria for the project required a 31 bar watertube boiler capable of generating 150 tons/h of steam firing bagasse (a by-product produced during the processing of sugar cane) or 120 tons/h of steam on coal while maintaining the steam temperature at 400°C - from 30-110% of boiler capacity on each fuel.

This required the design of a superheater capable of achieving this criterion. A two-stage unit with interstage de-superheating was eventually selected. The unique feature of the superheater is that the source of pure spray water for de-superheating is derived from the boiler itself utilising a feedwater condenser system. This 'sweetwater' condenser system was specifically designed by JTA for this project and eliminated the need to supply a demineralisation plant with its associated high capital and operating costs.

JTA's latest generation Continuous Ash Discharge (CAD) stoker was incorporated to achieve the high combustion efficiencies required when burning coal. To support the environmental requirements of the eastern Mpumalanga area, a wet gas scrubber is installed which reduces boiler emissions to below 120 mg/Nm3.

The design and customisation of the control system hardware by CS System Solutions consisted of a Modicon Quantum PLC communicating via the ModbusPlus protocol to existing PLCs and scadas on the plant and its own scada. The PLC is linked by means of an additional two ModbusPlus networks to the Modicon Momentum I/O modules grouped into specific areas of the boiler 6 plant.

"The Modicon Momentum I/O intelligent terminals were selected to engineer this project," says CS System Solutions Marketing Director, Piet de Villiers. "Utilising Momentum I/O modules offers substantial financial benefits - installation costs are decreased because of distances between hardware and field devices, and the saving from reduced cabling, racking and time sees a substantial contribution towards overall project costs and construction time."

Boiler 6 was commissioned at the end of October 1999 and has achieved all of the contracted performance, efficiency and emission criteria.

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System Integration & Control Systems Design

Sugar Industry clinches unique boiler design by CS Holdings in R38 million project

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