Refractometry: A Basic Understanding and Common Uses

A ray of light being refracted in a plastic block
(Courtesy of Wikipedia)

Refractometry, a combination of physics, materials, and chemistry, is the process which measures the composition of known substances by means of calculating their respective refractive indexes (RI). RIs are evaluated via a refractometer, a device which measures the curve, or refraction, resulting when the wavelength of light moves from the air into and through a tested substance. The unitless number given by the refractometer, usually between 1.3000 and 1.7000, is the RI. The composition of substances is then determined when the RI is compared to a standard curve specific to the material of the substance. There are also four separate types of refractometers: digital, analog, lab, and inline process. Although refractometry can measure a variety of substances, including gases and solids, the most common category of known substances to calculate are liquids; the inline process refractometer is used to quantify the makeup of liquids.

Refraction of a light ray
(courtesy of Wikipedia)

The ultimate focus of industrial refractometry is to describe what is in a final product or output of a process step. A field which relies directly on the results of refractometry is gemology. Gemological refractometry is crucial for accurately identifying the gemstones being classified, whether the gemstones are opaque, transparent, or translucent.

Other common examples of industrial refractometry uses are measuring the salinity of water to determine drinkability; figuring beverages’ ratios of sugar content versus other sweeteners or water; setting eye-glass prescriptions; understanding the hydrocarbon content of motor fuels; totaling plasma protein in blood samples; and quantifying the concentration of maple syrup. Regarding fuels, refractometry scrutinizes the possible output of energy and conductivity, and for drug-testing purposes, refractometry measures the specific gravity, or the density, of human urine. Regarding food, refractometry has the ability to measure the glucose in fruit during the fermentation process. Because of this, those in food services know when fruit is at peak ripeness and, in turn, also understand the most advantageous point in the fruit’s “lifetime” to put it on the market.

The determination of the substance composition of the product examples listed above all speak to the purpose of quality control and the upholding of standardized guidelines; consumers rely on manufacturers not only to produce these products but also to produce these products consistently and identically every single time. Therefore, the success of commercialism, etc. is dependent on maintaining the standards for the composition of substances, i.e. industrial refractometry.

Equipment manufacturers have developed numerous refractometer configurations tailored to specific use and application. Each has a set of features making it the advantageous choice for its intended application.

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MPR- E-Scan Inline Refractometer Settings and Readings Overview

The MPR E-Scan is an in-line process refractometer that directly measures the refractive index of process fluids and then displays the reading in any number of customer-desired units (Brix, Percent Solids, Dissolved Solids, SGU, R.I., etc.). A simple 0-10Vdc signal is used to transmit the reading from the sensing head to the electronics console, ensuring a robust reading that has a minimal chance of being effected by interference. The entire package is NEMA 4X rated and designed and manufactured with the best materials for each application to provide years of trouble-free service with a minimum amount of maintenance.

The video below provides and overview of zeroing, setting, and reading the refractometer.

Electron Machine Achieves ISO 9001:2015

The ISO 9001:2015 approval of a quality management system (QMS) means an organization demonstrates its ability to consistently provide products and services that meet customer and regulatory requirements, and aims to improve customer satisfaction through the effective application of the quality system, including processes for system improvement, and the assurance of conformity to customer requirements.

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies whose technical committees prepare and carry out the International Standards. ISO 9001 is the international standard that specifies requirements for the organization's quality management system. ISO 9001 was first published in 1987. The current version,  ISO 9001:2015, was released in September 2015. The previous version was ISO 9001:2008.

Organizations that are certified to ISO 9001:2008 should transition up to ISO 9001:2015 as quickly as reasonably possible, but the ISO Committee on Conformity Assessment has agreed to a three year transition period.

Electron Machine Corporation achieved ISO 9001:2015 as of November 2016.

Replace the Sensing Head on MPR E-Scan and MDS-Divert Systems

The MPR E-Scan is a rugged, industrialized, in-line process refractometer. It directly measures the refractive index of process fluids and then displays the reading in any number of customer-desired units (Brix, Percent Solids, Dissolved Solids, SGU, R.I., etc.).

The MDS Monitor Divert System is a BLRBAC compliant Black Liquor solids monitoring system designed specifically for Black Liquor recovery boilers.

The following paper illustrates the correct way to replace the sensing head on MPR E-Scan and MDS-Divert Systems from Electron Machine Corporation.

Electron Machine Refractometer Sensing Head Replacement from Electron Machine Corporation

Inline Refractometers Tough Enough for Paper Plant Black and Green Liquor Lines

Refractometer and HPC Adapter
with High Pressure Purge System

It's said the only thing a pulp and paper plant doesn't reuse is the "shade the building casts". The processes used in the production of pulp and paper are very efficient when you consider the reuse of energy and by-products. The efficiency comes at a cost though - through very hostile atmospheres and demanding operating conditions for process equipment.

For example, the "kraft process" (also known as the sulfate process) is the method to convert wood chips into pulp and then to cellulose fibers. This is done by mixing the wood chips with sodium hydroxide and sodium sulphate, soaking, cooking and processing.

Here's a very basic explanation of the kraft process. Wood chips are soaked and processed in sodium hydroxide and sodium sulphate mixture known as "white liquor". After the wood chips are impregnated with white liquor, they are then cooked in digesters to break the wood down into cellulose. The solid pulp is then separated and the remaining fluid is referred to as "black liquor". Black liquor is further processed to remove solids and chemicals which are to be re-used in the pulping process. One of the final by-products is "green liquor" which contains sodium carbonate and sodium sulfide and is then reacted with lime to regenerate more white liquor.

All of these steps expose instruments, process equipment, piping, and valves to very tough environments. Electron Machine Corporation, a manufacturer of extremely rugged inline process refractometers, has been actively refining the use of refractometers for measuring green and black liquor density for over 30 years.

The scaling associated with these applications results in an optical coating on the refractometer sensing head. If this scaling can be controlled to allow an acceptable duration of on-line measurement, and then effectively removed when coating occurs, the accuracy of the refractometer can be fully utilized with minimal maintenance. The primary issue then becomes the maintenance required to keep the cleaning system operating effectively.

Electron Machine's efforts led to a system using their "almost indestructible" MPR E-Scan Refractometer combined with heated high-pressure water for cleaning. The resulting combination provides an effective removal of optical coatings by reducing thermal changes and minimizing maintenance to allow for a reliable measurement source for on-line automatic control.

If you're interested in refractometry in pulp and paper processing, look no further than Electron Machine. They have the history, the experience, and the toughest inline refractometer on the planet.

For more information, visit http://www.electronmachine.com or call (352) 669-3101.

Inline Refractometers for Measuring Black Liquor Evaporation

Measuirng black liquor solids concentration.

Introduction:

Refractometers have long proven to be the instrument of choice for black liquor solids concentration. Electron Machine Corporation of Umatilla, Florida pioneered this technology to accurately measure black liquor dissolved solids 5 decades ago. Their MPR E-Scan inline refractometer provides digital accuracy with rugged components required for years of reliable use when installed in harsh industrial environments. This combination allows for easy integration into a mill-wide monitor / control system providing operators the information needed for efficient and easy-to-service control.

Application:

An important and overlooked area for refractometers is the pulp washing operation. By monitoring the concentration output the washers can be balanced to meet the needs of the evaporation process and a mill is able to regulate the mixing liquor. This control allows a consistent concentration supply to the evaporators and boiler. This installation is simple and greatly reduces hand sampling.

MPR E-Scan

Evaporation:

By installing the Electron Machine Corporation MPR E-Scan with Isolation Valve Adapters before and after each evaporator effect, the concentration and temperature output can be utilized to monitor efficiency, detect problems and operate economically. This monitoring allows control operators to adjust steam usage for optimal solids evaporation. Operators can determine if a quick flush cleaning can be performed to improve efficiency, prolonging the time between invasive, labor intensive cleanings. It also allows the detection of any problems before the liquor reaches the boiler, plus provides a consistent solids percentage for firing.

Conclusion:

With the addition of the Electron Machine Corporation MPR E-Scan to a mills process control system, a company can see increased profitability through the optimized control of steam usage, reduced labor cost from the reduction of offline hand sampling and the ability to prolong the time between labor intensive offline cleanings. This greater control provides more consistent firing solids allowing boilers to operator more efficiently.

Key Benefits:

• Consistent black liquor solids
• Minimize steam consumption
• Economical operation
• Optimize man hours
• Reduce costly evaporator cleanings