Felixton Sugar Mill - Cogeneration Upgrade

IN 2006 TONGAAT HULETT, THE OWNER/OPERATOR OF FELIXTON SUGAR MILL, WERE INVESTIGATING THE POSSIBILITIES OF INCREASING THE POWER EXPORT RATE FROM 3 MW TO AT LEAST 6 MW, AND POSSIBLY AS HIGH AS 8 MW.

However, the very nature of their cane feed system is such that the 8.5 MW of electrical load can, although unlikely, appear and disappear instantaneously. These load swings are caused by the whole-stick cane shredders and their application, and it is not unreasonable to have a conservative base load swing window of 5 MW when the shredders are running.

The load swing phenomena described above was mainly due to the inability of the existing mill turbo-generator governing systems to respond to load changes when the Factory is connected in parallel with the local Grid. Under parallel grid operation, the Grid would always take the load swings. It was reported by Tongaat Hulett that the turbo-generators became more unstable when the Factory was islanded (disconnected) from the Grid with the turbo-generators having to cope with the load swings alone. In this case, the Factory frequency became extremely unstable and was, in fact, a graphic mirror image of shredder load.

As consequence of the load swing phenomena it was evident to Tongaat Hulett that by increasing the export rate to 6 MW, the swing window would simply occur at a higher MW level, which would impact the ratings of the Factory/Grid interconnection transformers and may also have implications with cable and switchgear ratings.

Energy Power Consulting Engineers was requested by Tongaat Hulett to investigate and provide a possible solution. After an initial site inspection and audit, Energy Power Consulting Engineers proposed supplying new digital governing and voltage regulator systems. In addition to providing the equipment for the 3 x 10.5MW W.H. Allen Steam Turbine Generators (STG), Energy Power Consulting Engineers provided consultancy, detailed design, engineering and commissioning services for the upgrade of the turbo-generators and ancillary switchgear equipment.

The design and engineering services included:

• Project Management Plan

• Installation Specification Documents for Switchgear Upgrade and other associated installation works

• Work Method Statements for Switchgear upgrade

• Detailed Arrangement and Layout Drawings

• Detailed Schematics

• PLC I/O Drawings

• Cable and Termination Schedules

• Control System Functional Description

• Power Systems Analysis that included load flow, fault level, protection co-ordination, transient stability and harmonic studies

• Programming of Protection Relay settings and program scheme logic to ensure compliance in accordance with relevant standards.

The upgrade of Felixton Mill powerhouse and the re-arrangement of switchgear provided Tongaat Hulett a number of options with respect to the export of power to the Grid. The ability to base load a dedicated 10.5 MW STG, guarantees a constant export power profile. Conversely, in the event of a high factory load, a controlled bustie will allow all three 10.5MW STG’s to be paralleled and operate in load share mode, sharing the real and reactive power equally. The synchronization and load transfer across the controlled bustie and Factory/Grid Interconnector is

bumpless.

The Felixton Mill powerhouse was successfully completed and commissioned prior to the commencement of the 2008 cane crushing season. Energy Power Consulting Engineers would like to acknowledge the assistance of Tongaat Hulett Sugar and Turbine Generator Services (TGS) from South Africa who assisted with the commissioning.