Measurement Automation Strategy: Key to Bio-Ethanol ... - Krohne

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KROHNE White Paper Measurement Automation Strategy Key to Bio-Ethanol Refinery Efficiency By Hemant Narayan cellulosic. The goal of the rectification process is to achieve maximum purification (up to 190 proof). Then the dehydration process employs molecular sieves to convert the 190 proof ethanol into 200 proof ethanol, going from 5% moisture content to 0%. If the process fluid moves too quickly through the molecular sieves and some moisture remains, then the entire batch must be run back through the dehydration system again – a completely inefficient step that wastes energy and ties up production capacity and potentially causes a bottleneck for the entire plant. To avoid this problem, a plant could extend the dwell time in the molecular sieves to ensure that all moisture is removed. However, this margin of comfort comes at a cost in terms of productivity loss and unnecessary energy consumption. Alcohol proof measurement of rectifier output (190 proof) and dehydration output (200 proof) can dramatically improve process efficiency. Precise density measurements, detects exactly when the ethanol reaches the anhydrous threshold (zero moisture content), so that the dehydration process can meet its target without overreaching, thereby obviating the need for any wasteful comfort margin. As with the percent-solids measurement application discussed above, the new generation of Coriolis meters with single, straight tube design, has proven to be a highly accurate and reliable solution for realtime monitoring of alcohol proof during the rectification and dehydration processes. The continuous trends data allows for instantaneous correction of process upsets and ensures the consistent and tight control of proof values in final product. This process control is critical to meeting quality control specifications and to increasing throughput and profitability. An important advantage of the state-ofthe-art Coriolis meters, such as the KROHNE 7000 Series T80 OPTIMASS meter, is the ability to measure multiple parameters in a single device – proof, density, temperature and flow. Previously, plant operators needed to purchase, install, calibrate and maintain several separate devices to perform all these functions: typically one meter would measure density and proof on a slipstream, and additional instruments would be installed in the main line to measure temperature and flow. More Efficient Dryer Operation Single straight tube Coriolis meters, with multiple-parameter capability, also provide high pay backs when installed on the evaporator syrup draw. Installations of an online flow/density meter at the intermediate and final stages of the evaporator process have successfully demonstrated significant reductions in energy consumption, by February 20, 2008 8 of 12
KROHNE White Paper Measurement Automation Strategy Key to Bio-Ethanol Refinery Efficiency By Hemant Narayan tightly controlling the syrup percent and flow rate through the evaporators. Running syrups at higher solids is desirable, because less moisture means less work for the dryers and therefore lower energy consumption in the drying process. Higher solids percentage (i.e., lower moisture content) can be achieved by reducing the flow rate through evaporators which increases retention time. Unfortunately, lower flow rates can cause extensive build up inside the lines and can also affect the evaporator efficiency, and line plugging can cause costly downtime. For these reasons, plant operators need to manage the process to maintain the optimal solids level at all times. As with other processes, the continual, automated measurement by coriolis meters facilitates better control than offline lab samples. The single, straight tube design of the KROHNE Coriolis meters mitigates the maintenance and reliability problems that can plague conventional "bent tube" Coriolis meters, especially given the high solids content and viscosity of the syrup. The KROHNE Coriolis meters employ adaptive sensing technologies (AST), a patented design makes accurate measurements even of mixtures with high viscosity or solid matter content and the straight-tube design causes less pressure drops than other flowmeters, resulting in lower energy costs. Volumetric Flow metering Upstream of fermentation, dry-milling ethanol plants make extensive use of inline electromagnetic flowmeters to measure flows containing high solids content, such as backset, corn slurry, mash, beer, as well as on whole, thick and thin stillage. Most magnetic flowmeters available in the market today use a pulsed DC technology which has replaced older AC technology that had inherent problems with drift and zero stability. However, pulsed DC magnetic flowmeters have performance limitations, especially with noisy applications such as slurry. These problems can be addressed by using the KROHNE IFC3000 signal converters with digital noise filtering and a low-noise electrode configuration. For demanding, highsolids applications, KROHNE’s advanced magnetic flowmeters provide self-diagnostic capabilities for detecting sensor coating degradation and predicting electrode or liner failure, in order to minimize failures and expensive downtimes. The multiple-parameter capability of some magnetic flowmeters, such as the KROHNE OPTIFLUX 4300C, provides an added benefit during CIP procedures. The CIP wash includes flushing the lines and recirculation chemical in a specific sequence, such as acid-wateralkali-water. By using the conductivity measurement feature built into the flowmeter, the process can be February 20, 2008 9 of 12
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