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“Operating certain process streams at low sugar concentrations [inferred by relatively low-density measurements] can cause inefficient processing and poor crystallization. Streams operating at high sugar concentrations [inferred by relatively high density measurements] can cause inefficient processing, and create operational problems, such as crystal sugar deformation, machine and inversion problems,” adds Pedro Collegari, general manager at Grupo João Lyra’s Vale do Paranaíba plant, Capinopolis, Minas Gerais, Brazil.
|FIGURE 2: Inline Density/Concentration Transmitter Installation|
|Inline differential pressure probes operate similarly to those used in vessels.
Improved inline density measurements allow Collegari’s plant to operate in the proper range of concentrations on a consistent basis, and improve product quality. Collegari uses differential pressure probes and U-tube densitometers for accurate density measurement. Radiation densitometers aren’t based on physical property of density, but rather on the amount of radiation that travels through the material. This amount depends on the material density in these applications, but also is affected by the temperature of the material. This means measurement errors can occur when operating the instrument at a different temperature than that at which it was calibrated. Therefore, Collegari doesn’t have radiation densitometers in his plant because their accuracy suffers over many temperatures in his applications.
Biomass from the Beginning
In their early days, instrumentation manufacturers often initially focused on one niche or industry before expanding into others. Examples of this include Bailey Controls (boilers), Fischer & Porter (rotameters), Foxboro (recorder/controller), Honeywell (furnace regulation), and Taylor (weather measurement).
On the other hand, “SMAR has focused on the biomass processing industry since it was founded in 1974,” says Cesar Cassiolato, marketing director at SMAR, Sertãozinho, Brazil. “This was primarily due to its location in a town surrounded by fields of sugarcane and refineries. Using sugarcane to produce fuel has been steadily increasing since the 1970s, in part due to government policies that promoted the production of fuel-grade ethanol from locally grown biomass to displace imported gasoline. Increased production of ethanol fuel from sugarcane has helped Brazil become self-sufficient with regard to imported oil (on a net basis).”
Usina’s Muraishi says that his plant has “various types of measurements including flow, level, pressure, temperature, concentration, pH and conductivity. In particular, differential pressure density instruments measure sugar concentration and the alcohol concentration of intermediate and output alcohol streams from the distillation and dehydration columns. These measurements have significantly increased the productivity of the plant.”
Collegari concurs and adds that in the past, “New processes simply were not implemented because of the inability to control the process. Improved instrumentation and control strategies now allow the plant to reap the benefits of new processing techniques and the implementation of more advanced control strategies. Overall, improved online measurements and better control have increased plant production by at least 25% in the past five years.”
Cassiolato adds, “Over the years, SMAR has developed instruments for biomass processing, including a transmitter that hydrostatically measures the density of liquids in a range of ±0.5 to ±5.0 by inserting a temperature-compensated probe with two pressure sensors into a tank. Also, close proximity to these plants has generated considerable process knowledge that has resulted in automation projects that improved product quality and production efficiency in more than 90% of sugar and alcohol plants in Brazil, and made SMAR a leader in this market. As a result, instrumentation and automation has been crucial to making the area surrounding Sertãozinho reputedly the most productive sugar growing/producing/refining region in the world.”
Greg Loest, director of engineering at ICM, Colwich, Kan., says, “We’ve noted that additional levels of automation, such as better instrumentation, programming logic and/or valves, have made our plants easier to operate and more consistent, while improving their overall energy efficiency,” ICM has designed approximately 75% of the ethanol plants in the USA.
Cassiolato adds that performance benchmarks improved in Brazil between 1977 and 2005. Fermentation yield went from 75%-80% to 90%-92%; distillation yield from approximately 95% to over 99%; fermentation time was cut from 18 hours-22 hours to 6 hours-10 hours; and sugar extraction from sugarcane increased from approximately 88% to 98%.
Working at a sugar plant that has been making alcohol for fuel for over 25 years, Marcos Antonio Barreto, production manager at Usina Mandu, São Paulo, Brazil, says, “Hydrostatic density measurements are also used to infer the interface level in decanters to control the withdrawal of the heavy phase. Proper interface location is important to achieve good decantation and removal of impurities.”
Proper elimination of impurities is the key to efficient plant operation. Measurement and control of pH is important to enhance the separation of impurities. “Our process has various acid additions. Neutralization of the process streams after these additions is important for efficient decanter operation because poor pH control increases the amount of impurities fed to the downstream processes. These tend to upset the operation, cause product losses and degrade plant efficiency,” says Barreto.