Control Engineering Online Update for September 15, 2006

By Control Engineering Staff September 15, 2006
Highlights Sponsored by ipd
La Pastora sugar mill in Lara, Venezuela, burns sugar pulp as fuel and uses 80% recycled condensed water in its boilers. The decision has placed the company far ahead of its competition and resulted in a substantial return on investment. According to the company, the system has been running two years, and “after paying for itself in just 60 days, it’s been allowing La Pastora to put money in the bank ever since.”

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Sweet Savings from Sophisticated Reuse Operations

In sugar processing, the natural sugar stored in cane stalk or beet root is separated from the rest of the plant material. For sugar cane, this is accomplished by pressing the cane to extract the juice, boiling the juice until it begins to thicken and sugar begins to crystallize, and then spinning the crystals in a centrifuge to remove the syrup. The resulting raw sugar is then shipped to a refinery.

The La Pastora sugar mill in Lara, in the central west coastal region of Venezuela, sets itself apart from others not only by its superior sugar processing operations, but also by its sophisticated recycling/reuse operations. It uses the by-products of sugar processing for power generation.

La Pastora sugar mill realized such substantial savings by using 80% recycled condensed water in its boilers, the automation system to control the process paid for itself in two months.

‘After the sugar cane is pressed and the juice extracted, you’re left with a great deal of pulp,’ explains Antonio Hernández of Ingenería Automatización y Control (IAC), the systems integrator for the La Pastora project. ‘This pulp would normally be discarded. But what they’re doing at La Pastora is using it as an alternative fuel source and burning it to help power the generators.’

La Pastora’s diesel generators are powered by diesel fuel, of course, but its steam generators use a combination of diesel fuel and sugar pulp. In a similar fashion, La Pastora reuses the water by-product created by its steam generators. But the company needed a better way to monitor, control and regulate the recirculated water.

‘La Pastora’s water recovery system used to recirculate condensed water directly to the boilers,’ states Giovanni Montes, Business Director at IAC. ‘But this was proving to be hazardous to the health of the entire system, partly because debris from the sugar cane processing was getting through. The system we designed, among other things, gives La Pastora supervisors an easy way to determine if there are solids in the water and to start and stop processes automatically.’

Critical Requirements
‘In the steam-generating process of La Pastora’s boilers, it’s very important that the water used for boiling have certain attributes,’ says Hernández. ‘For example, it needs to be free of solids and residue that might cause clogs. It also needs to be free of oxygen, which can cause rust and corrosion and shorten the lifespan of the boilers’ internal pipes and plumbing.’

To ensure that these criteria are met, the condensed water produced during the steam-generation process is stored in tanks where it’s chemically treated. Then, it’s transported to a de-aerating machine before being sent back to the steam generator’s boilers. La Pastora has a total of five tanks for the storing of processed ‘good’ water plus an additional tank for crude water.

To control and regulate all recycling and dispersal of the condensed water, IAC chose an Opto 22 SNAP Ultimate I/O system, which consists of a SNAP Ultimate brain and rack, two analog input modules, one serial module, eight digital input modules, and eight digital output modules. IAC designed the control architecture, procured all the hardware, completed the installation, and developed the control strategies with ioControl, the programming software included with the SNAP Ultimate I/O system. (The Opto 22 components were sourced from Grupo Telebaud C.A., a distributor that serves integrators throughout Venezuela and the rest of South America.)

Control and Cost Savings

To control and regulate all recycling and dispersal of the condensed water, IAC chose an Opto 22 SNAP Ultimate I/O system sourced from Grupo Telebaud C.A., a local distributor.

The system collects data from the water recovery system’s processes. For example, pH and oxygen reduction potential (ORP) sensors connected to analog input modules provide data on the concentration of undissolved, suspended particles present in the water. This data is aggregated and evaluated by the intelligent SNAP Ultimate controller, which begins or delays the delivery of the water to the de-aerator accordingly. The SNAP system also controls the chemical dosers that treat the water, as well as and a series of pumps and valves that bring well water (also used for the boilers) from its source to the mill.

La Pastora uses Opto 22’s ioDisplay software to design human machine interface (HMI) screens that visualize the described processes and present the data in easy- to-understand graphical representations. An OptoTerminal-G75 operator interface terminal lets La Pastora personnel view data, modify process parameters, adjust setpoints, and start and stop processes locally.

La Pastora’s decision to implement a new automation system solely to help the mill use water by-product and sugar waste to its advantage has placed the company far ahead of its competition and resulted in a substantial return on investment. By itself, the savings from using 80% recycled condensed water in the boilers allowed La Pastora to pay for its new system in a mere two months time. La Pastora management estimates that the savings from the burning of sugar pulp has been even greater. According to Hernández, the system has been ‘up and running perfectly for two years. After paying for itself in just 60 days, it’s been allowing La Pastora to put money in the bank ever since.’