The Santa Matilde sugar cane processing plant in the Honduras is enjoying the sweet taste of success thanks to ABB’s variable speed drives (VSDs). In fact, the plant is now so energy-efficient that it sells its excess electricity into the local grid – bringing in an extra one million dollars (US) of income every year.
The reason for this impressive improvement is that previously the plant’s cane-crushing machinery was driven by steam produced by burning bagasse - the fibrous waste product left after sugar cane is processed.
But now the steam is used to propel turbines that generate electricity. And that electricity feeds the new ABB ACS1000 VSDs and induction motors, providing the plant machinery with both exceptional energy-efficiency and precision control.
The customer is satisfied with the results. Ing. Jorge Arriaga from the Santa Matilde plant, said:“
We are very pleased with the performance of ABB’s ACS1000 variable speed drives. The overall energy efficiency of the Santa Matilde plant has increased tremendously. Today, we are not only energy self-sufficient, we have also increased our annual revenues by approximately one million dollars by selling excess energy to the grid. Furthermore, the process runs much smoother than before.”
Crushing cane since 1938
The Santa Matilde plant belongs to Compania Azucarera Hondureña S.A., founded in 1938 and one of the largest sugar companies in Honduras, Central America. The plant operates 155 days per year during the sugar cane harvest period from November to May, and can process 10,200 tons of cane per day. It is aiming to increase its capacity to 12,000 tons per day.
Traditionally, sugar cane plants burn their bagasse to produce steam that is used to both generate electricity as well as running the steam turbines that drive the cane-crushing mills. This virtuous energy circle means that, under normal operating conditions, there is enough electricity produced locally to satisfy the plant’s total energy requirements with sometimes enough left over to export into the grid.
The cost of electricity in Honduras is relatively high because it is mainly produced by fuel oil. Therefore, it became a very attractive financial proposition for the Santa Matilde plant to make the optimum use of the energy it produced to create a greater surplus available for selling into the local grid.
The switch from steam to electrical power - payback in only a year
In the past, the Santa Matilde sugar plant needed five 750 kW steam turbines to drive the cane mill, resulting in a total power demand of 3,750 kW. Each turbine required 35 pounds of steam to produce 1 kilowatt (kW) of power - so about 131,000 pounds of steam were required to drive the complete cane mill.
In contrast, turbines with high-pressure boilers, dedicated to power generation, require only 12.7 pounds of steam to produce a kilowatt. Clearly, there was a major efficiency advantage to be gained by transitioning the production process to operate on electricity.
The steam turbines that were driving the cane mill have therefore been replaced by ABB ACS1000 medium voltage (MV) variable speed drives and induction motors. This now enables the steam to be used exclusively to generate electricity, resulting in an additional energy generation of 10,300 kW/h, which is used to feed the drives.
Furthermore, excess energy of about 6,550 kW can be sold to the grid. This creates about one million dollars (US) a year of additional revenue for Compania Azucarera Hondureña S.A., resulting in a payback time for the MV drive investment of about one year.
Lower maintenance and enhanced reliability
The switch to electricity has also delivered a number of operational benefits. For example, the smooth ramp-up provided by the VSDs protects the mechanical equipment, thus prolonging its lifetime and reducing maintenance costs.
The noise from the electrical machinery is also almost negligible compared to that of steam turbines and the drives require only a fraction of the maintenance needed by maintenance-intensive steam turbines. This results in higher uptime and further reduces maintenance costs.
The ACS1000 VSDs also incorporate a ride-through function that enables the plant operation to withstand short-term disturbances in the power supply. And, after a shutdown, the cane mill can return to full operation much faster than when it was driven by steam.
Optimized speed control and overload protection
The ACS1000 controls the speed of the mill depending on the amount of cane being crushed. Furthermore, it can regulate the torque to maintain the optimum speed.
The VSDs also protect the mill against an overload by using their built-in capability to monitor the shaft torque. In case of an overload, this enables the mill to be driven in reverse to remove the excess cane and resume normal operation with minimum production loss.
