Measuring Concentrations in Solutions
Solid dissolved in a liquid
or
Liquid dissolved in another liquid
RHOTEC (density measurement) and SONATEC (sound velocity measurement) are used for a two component solution.
(A two component system can be a solid dissolved in a liquid or a liquid dissolved in another liquid.)
These applications are common where a media such as sugar, salt, alcohol, etc. is dissolved in water.
(Also most acids and caustics are aqueous – water based – systems.)
To determine the concentration of extract and alcohol, density and sound velocity are measured simultaneously. This is done by COMBITEC – a combination of RHOTEC and SONATEC (two sensors in one).
(Density measurement allows calculating the concentration of alcohol while the concentration of extract is calculated based on sound velocity measurement.)
Also note Centec offer RHOTEC and SONATEC in an explosion proof version, so they can be used in ATEX (explosive atmosphere) environments.
Attached you find some reports describing common applications related to two and three component systems. As you see, they are found in different industries.
For applications in chemical industries it is extremely important to know the type of acid/caustic as well as the concentration / temperature range of the measurement.
(The selection of the sensor material which is resistant against the acid/caustic. e.g. stainless steel, hastelloy, monel, incoloy, tantalum)
Oxygen Measurement
Optical oxygen measurement is state of the art and provided by Centec and several of our competitors. However, many sensor manufacturers offer Clark electrodes to determine the oxygen content in the product. Therefore, you should know the principle of both technologies and the advantages of the optical method.
Optical method
Optical oxygen sensors contain a small glass component (“optical window”) installed in the measuring head. On the surface of the optical window there is thin film of fluorescent molecules. A polymer optical fiber transmits excitation light (blue-green-light) from the light source to the fluorescent molecules. When the molecules absorb this blue-green-light they are promoted to a higher energy state. After a certain time they convert back into a lower energy state during which a detectable red light is emitted. The same polymer optical fiber transmits this red light to the measurement device.
If oxygen is present the energy is transferred from the excited fluorescent molecules to the oxygen. Thus, the detected red light decreases according to the oxygen content. Centec offers an in-line oxygen sensor (OXYTRANS TR) and a portable device (OXYTRANS M). Both of them use the optical method.
Clark electrode
Clark sensors contain two electrodes which are linked by a potassium chloride solution (KCl) serving as electrolyte. One electrode consists of platinum (Pt); the other one consists of silver (Ag). When a small constant voltage is applied across the two electrodes the Pt becomes negative (> cathode) and the Ag becomes positive (> anode). The electrolyte and the product are separated by a thin membrane which is permeable to oxygen. The partial pressure difference of oxygen between both sides of the membrane is the force “pushing” the oxygen from the product through the membrane into the electrolyte.
At the cathode, electrons are “consumed” by the reaction with H2O and O2 which leads to OH-. At the anode, silver reacts with Cl- from the electrolyte to produce AgCl and free electrons. The silver chloride (AgCl) deposits on the surface of the silver electrode. The OH- produced at the cathode combines with the K+ from the electrolyte, so the electrolyte changes from KCl to KOH. The free electrons generated at the anode flow through the circuit to the cathode resulting in a current that is proportional to the concentration of oxygen (see attachment).
Disadvantages of the Clark method
Due to the consumption of Cl-, the electrolyte needs to be replaced frequently
The membrane is sensitive to pressure shocks and fouling, so its lifetime can be short
Removing the AgCl deposits from the anode is a time-consuming procedure
Frequent calibration results in high upkeep and labor costs
Oxygen is consumed from the product during the measurement
There has to be a constant product flow to avoid inaccurate readings
After disconnecting and connecting again, the sensor can need hours for polarizing
Clark sensors are less accurate compared to optical oxygen sensors
CO2 Measurement
It is mainly in food and beverage manufacturing where CO2 needs to me controlled.
Centec offers two types of CARBOTEC sensors for CO2 measurement:
(1) Pressure/temperature method
(CARBOTEC TR-PT)
The concentration of CO2 dissolved in a liquid is determined in a closed volume (sensor head) by measuring the pressure and temperature when a state of equilibrium between the liquid and the gas in the sensor head exits. CARBOTEC calculates the content of CO2 in the liquid by applying a product CO2 specific formula.
(2) Optical method
(CARBOTEC NIR)
CO2 is measured selectively and uninfluenced by other gases based on Attenuated Total Reflection (ATR). While passing a crystal, a beam of infrared light is reflected at the surface which is in contact to the carbonated liquid. Each time the beam is reflected, the CO2 molecules absorb some of the light. By intensity measurement of the infrared light, CARBOTEC NIR precisely calculates the CO2 concentration.
Without any moving parts in the sensor, CARBOTEC NIR is basically free of maintenance. It allows determining true CO2 content even when there is a mixture of gases in the liquid!
Centec Summary:- cold block engineering & automation, water treatment, water deaeration, wort aeration, yeast pitching, carbonation, carboblending, nitrogenation, liquid blending, flash pasteurization, dealcoholization, cleaning-in-place, oxygen measurement, carbon dioxide measurement, determination of concentrations by measuring density and sound velocity.
CO2 content has a strong influence on the quality and taste of alcoholic and nonalcoholic beverages. Therefore, CARBOTEC is a crucial instrument for manufacturing beers, sparkling wines, soft drinks, mineral waters and all other types of carbonated products.
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Mass Flow meters versus RHOTEC
Centec is often asked if they provide mass flow meters. The answer is “no”. Read on.
A mass flow meter can be used to determine density. However, customers requiring high accuracy may be interested in Centec’s density sensor RHOTEC.
So keep in mind, RHOTEC could be an alternative to a mass flow meter.
And RHOTEC allows determining the concentration of a media dissolved in a liquid based on the relationship between density and concentration.
RHOTEC (in-line version) RHOTEC – E
RHOTEC L = Lab RHOTEC L
There is a nice description of the working principle of a Mass Flow Meter HERE
RHOTEC is about ten times more accurate than a mass flow meter. This is due to the very high frequency we apply for density measurement.
De Alcohol Technology
For decades, the largest brewery groups in the world have trusted Centec technology. Centec equipment is used throughout the entire brewing process. One of our core competencies is the fully automated and aroma conserving dealcoholization of beer, wine and fermented products.
DeAlcoTec is a fully automated system for aroma conserving dealcoholization of beer, wine and fermented products.
Centec’s latest technology, tested in close cooperation with Weihenstephan, incorporates a very specific and highly efficient method for aroma recovery during the dealcoholization process.
Other features include e. g. in-line carbonation and recording of all relevant quality parameters of the product as well as the simultaneous rectification (concentration) of extracted alcohol up to 90 % ABV.
The specific benefit of Centec technology is extremely gentle processing at low temperature with a short retention time, thereby optimizing product defining aroma and flavour profiles. A residual alcohol content of 0,01 % ABV can be reached.
Sugar Production
During sugar manufacturing, sugar concentration can be measured and controlled with extremely high precision with our density sensor RHOTEC and our sound velocity sensor SONATEC.
The SONATEC is in operation at Grupo Pantaleon in Guatemala
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