By replacing cascade converters with four ABB ACS 5000 variable speed drives to control the speed of induced draft (ID) fans at the Saraburi cement plant, Siam City Cement Company (SCCC), Thailand's second-largest cement producer, has made energy savings of $250,000 a year.
The drives, each rated at 2.5 megawatt (MW), control the flow rate of hot gases from the kiln to a series of cyclone chambers in a preheater tower designed to preheat the material before it enters the kiln to save energy.
The ID fans are a major consumer of electrical energy and were previously controlled by sub-synchronous cascade converters, which have a restricted operating range that limits the plant’s production capacity. Here the fan’s speed was controlled in the range of 60 – 100 percent of their maximum, but using the new drives solution they could be operated across the full range 0 – 100 percent, offering greater production flexibility to the cement plant’s operators.
Operational costs of the plant were also affected by the age of the cascade converters since the carbon brushes on the machines needed replacing every few months and spare parts were becoming scarce. To replace the brushes, regular shut downs were required to ensure the cascade converters could maintain operation 24 hours a day to fulfill the continuous cement production requirements of the plant. These shut down periods involved switching off the kiln, which cost several thousand dollars a time.
Motor and preheater ID fan at Siam City Cement’s Saraburi cement plant
ACS 5000 variable speed drives controlling the flow rate of the preheater ID fans
The immediate effect of installing ABB’s ACS 5000 variable speed drives on the plant was that annual energy costs were significantly reduced resulting from a 2,500 MWh saving in electricity consumption per year, which reduced CO2
emissions per year by about a 1,250 tons. Furthermore, lower maintenance and greater reliability reduced the number of required plant shut downs and, due to the removal of slip rings on the existing wound rotor motors, which were no longer required, further maintenance cost reductions could be made. In addition, ACS 5000 variable speed drives feature a ride through function, that enable the drives to operate continuously even during prolonged network supply voltage fluctuations, which also helps the plant improve its production capacity.
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