Tower Hill Sugar Mill - 31.5 MW Cogeneration Plant Project

Energy Power Consulting Engineers were engaged by Shanghai SFECO Trading Co. Ltd to provide consultancy and design expertise for the construction of a new 31.5MW Cogeneration Plant located immediately adjacent to the existing Tower Hill Sugar Mill in Belize, Central America. With a large amount of excess bagasse available from Tower Hill Sugar Mill, a decision to construct a new 31.5MW Cogeneration Plant adjacent to the Tower Hill Sugar Mill was made and a Contract was awarded to a Chinese company, Shanghai SFECO Trading Co Ltd.

Initially Energy Power Consulting Engineers provided Process and Instrument Diagrams (PID’s) for the new cogeneration plant before being asked to expand its involvement and carry out a complete Power Systems Analysis. In addition, Energy Power Consulting Engineers was also asked to design and supply customized control panels comprising Si-TEC Xtend digital control and governing equipment for a 15 MW Extraction/Condensing Steam Turbine Generator, 12.5 MW Backpressure Steam Turbine Generator and two 2 MW Reciprocating Engine Generators (EG’s). The STG’s were supplied by Hangzhou Turbine Company and the EG’s by Ningbo with both equipment suppliers being Chinese. Very late in the project, Energy Power Consulting Engineers was also asked to supply Basler Electric DECS 200 Automatic Voltage Regulators for the STG’s and the EG’s.

The design and engineering services included:-

• Process and Instrument Diagrams for the entire cogeneration plant

• Detailed Arrangement and Layout Drawings for the STG and EG control panels

• Detailed Schematics for the STG and EG control panels

• DCS I/O interface drawings for the STG and EG’s

• Control System Functional Description for the entire cogeneration plant

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

The Cogeneration Plant is designed to supply power to the Tower Hill Sugar Factory and the Utility Grid network, which is managed and operated by Belize Electricity Limited. For the purposes of meeting the Contract performance guarantees, the Cogeneration Plant exports 13.5 MW of power to the Grid. The steam cycle while the Tower Hill Sugar Factory is in crop (and also during the early part of the out crop), allows the total 13.5MW of export power to be met by only the STG’s. During the crop, the EG’s will generate in parallel with the STG’s at a reduced rate thereby saving bagasse fuel and providing an additional quantity of bagasse for out-of-crop storage.

During the out of crop, when the stored bagasse runs low, the EG’s take over and generate all the power requirements for the Cogeneration Plant and Sugar Factory. There will be no export power to the Grid when the bagasse supply has been exhausted.

In normal running mode when Tower Hill Factory is in crop, the intention is for the 12.5 MW backpressure STG will generate in base load at a pre-set kW load reference of 11.5MW. The 15 MW extraction/Condensing STG kW reference will vary to meet the export load and the Sugar Factory electrical load not displaced by the 12.5 MW STG. Typically the 15 MW STG generates at a nominal kW load of 12.7 MW, meaning the combined total generation load including the contribution from the EG’s will be 25.2 MW of which an average 13.5 MW is exported to the grid and 11.7 MW to the Sugar Factory and Cogeneration Plant.

With the 12.5MW STG is selected for base load mode, it provides the bulk of the uncontrolled Low Pressure (LP) steam requirement to the Tower Hill Sugar Factory with the balance provided by the 15MW STG using the controlled extraction valve.

The LP steam range pressure will vary with factory process demand. When the process demand exceeds the extraction/condensing capability of the 15MW STG and the kW reference for the 12.5MW STG is at maximum, the DCS will enable the HP-to-LP steam reducing station, opening the control valve and allowing more HP steam to pass through the let-down station until such time the LP steam pressure range is at the correct pressure. The DCS will be programmed so that the operation of the HP-to-LP steam reducing station, and the amount of steam let-down through this station, is minimised to improve the efficiency of the plant in so far as the Sugar Factory operating conditions permit.

The commissioning of the new 31.5MW Belize Cogeneration Plant was successfully completed and commissioned.