Supplementing lab analysis with inline measurements
Coriolis flowmeter provides multiple measurements
A single Coriolis flowmeter can measure a number of parameters simultaneously, often eliminating the need for multiple instruments. Their highly accurate measurement of mass flow and density (up to 0.05% on mass flow and 0.0005 g/cm3 for density) makes Coriolis ideal for many process control applications.
Often overlooked by many instrument and process engineers is the ability of Coriolis flowmeters to be used for quality control. For example, the flowmeter’s density function can be used to measure Brix and Plato values to ensure the quality of the ingredients being used. The viscosity option provides continuous measurement to minimize off-spec product between lab measurements.
One food plant installed a Coriolis flowmeter (Figure 2) in a continuous bypass line of a batter mixing tank. The batter, consisting of flour, water, and additives, is mixed until the correct viscosity is reached, and then pumped to the production tank for processing. The resulting savings in ingredients and the improvement in product quality paid for the installation in less than six months.
Instrument diagnostics detect problems
Diagnostics enhance measurements by alerting operators to abnormal process conditions or upsets. For example, entrained air in the line can cause process problems. An operator needs to know if external air is being drawn in through a leaking seal, a cavitating pump, or an empty balance tank, because air in the process can affect product quality.
A Coriolis flowmeter does not operate properly with large amounts of entrained air, so it has diagnostics to detect this condition. In an E+H Coriolis meter, a diagnostic value shows that tube oscillation is in a good range, indicating no entrained air. If air appears in the line, the diagnostic value will change (Figure 3), setting off an alarm to the operator.
The same function can be used to improve accuracy when starting from an empty line. The automation system can use the diagnostic information in combination with a downstream control valve to automatically increase back pressure during start-up, and then gradually decrease back pressure once the air is gone from the system.
The first step is to evaluate all the lab measurements and determine what can be replaced or supplemented with inline instrumentation. The goal is to help the lab focus on the final and critical food safety and quality measurements, while the instrumentation is used for real-time operations. Considerations here include:
- How much time is being spent taking manual grab samples?
- How much time is being spent running lab analyses?
- How many workers are needed for these tasks?
- How quickly does manual sampling detect process changes?
- How much do the delays in obtaining manual results affect product costs?
The hydro cooker application discussed earlier is a good example of a plant that saved workers’ time by eliminating two grab samples per hour, and then saved on disinfectant chemical costs with timelier inline analysis. The next step is asking which of the inline measurements would benefit a particular process.
For example, dissolved oxygen measurements in brewing, wine, and juice production minimize oxidation of the product. Measuring the Brix of tomato paste can help control the amount of paste to be added during cutting. Viscosity measurements can improve the product consistency of batter coating for beans, onions, meat, poultry, and other products.
Inline process analyzers cannot replace all the functions of a modern lab in a food plant, as certain measurements can’t yet be reliably made by inline analyzers and instruments. However, modern inline process analyzers and instruments can reliably replace or supplement many of the measurements traditionally made in a lab.
Moving from offline to inline measurements cuts labor costs by eliminating manual sampling and analysis, and it adds consistency by automating the measurement process. Inline measurement delivers results in real time, allowing automation systems to adjust process parameters continually to optimize quality and increase throughput.
Ola Wesstrom is food and beverage industry manager for Endress+Hauser.
Subscribe to the Process Instrumentation & Sensors eNewsletter at www.controleng.com/newsletters
- Evaluating the quality of food and beverage production has traditionally depended on lab analysis.
- Many of the same analyzer technologies used in labs have now been adapted for online use in a plant environment.
- Certain types of process instruments, such as Coriolis flowmeters, can perform specific analysis tasks.