Common Industrial Refractometer Applications and Processes

Industrial Refractometer
Refractometers measure a dissolved material's concentration in a liquid. There are numerous prospective applications in various industrial sectors. Even if the production, environmental and processing processes differ from sector to sector, despite the end product, all fundamental unit operations and control strategies are approximately the same. Outlined below are several of the more common applications and processes where inline industrial refractometers are used.


In industry, crystallizers are used for liquid solid separation. They are an important component of chemical processing equipment as they can generate high-purity products from a relatively low energy input. To determine the right seeding point (evaporative crystallizer) or to detect when crystals start to form (cooling crystallizer), the refractometer controls the liquor concentration.


Industrial RefractometerProcess reactors are used for commercial production applications in adhesives processing, agriculture, chemical processing, cosmetics, food and beverage production, paints and coating production, paper and pulp processing, pharmaceutical and medical production, plastics and thermoplastics processing. The real-time progress of a reaction can be followed using inline refractometers, either through the leveling out of key process variables, or the reaching of a single component's targeted refractive index value.


An evaporator is a tool used in a method to transform the liquid form of a chemical substance such as water into its gaseous / vapor form. During that phase, the liquid is evaporated or vaporized into a gas form of the intended substance. Inline refractometers provide real-time data of concentration changes in the process media.

Reverse Osmosis

Reverse osmosis (RO) is a water purification method that removes ions, unwanted molecules and bigger particles from drinking water using a partially permeable membrane. Inline refractometers provide real-time data of concentration changes in the process media.

Spray Dryers

Spray drying is a way to produce a dry powder from a liquid or slurry by drying quickly with a warm gas. This is the preferred drying technique for many thermally sensitive products like foods and pharmaceuticals. A consistent distribution of particle size is a reason why certain industrial products such as catalysts are sprayed. Process refractometers monitor the concentration of the feed line to the spray dryer, ensuring correct particle size after drying, improving quality, and increasing product shelf life.

Dissolving Tanks

Dissolving tanks are used to dissolve solids into a liquid, thereby changing the concentration of the solution. Refractometers provide continuous measurement of the concentration components in solution as the solute dissolves into water or solvent. Information for dissolving rate and dissolved solids is provided instantly through the refractometer and corresponding electronics.

Solid / Liquid Extraction

Solid / Liquid extraction method is a very popular method in the pharmaceutical, cosmetic and food industries to acquire natural ingredients such as natural raw material flavors and fragrances. Inline refractometers are used to detect the amount of extracted substance (dissolved solids) in the liquid after the extraction process. The measurement by the refractometer is not affected by undissolved solids, only by the dissolved matter, making it ideal to follow extraction efficiency.

Cooking Processes

The art, technology, science and craftsmanship of preparing food for consumption is cooking. The large scale production of juices, jams, jellies, dairy, and fruits in modern production facilities require automation and control instrumentation for quality and efficiency. Sugar is a key component in many foods that needs to be monitored. The inline refractometer is used to monitor refractive index of the product, and when when cooking is complete. Inline refractometers determine the end of the cooking process based on qualitative measurements of dissolved solids.

For more information about using applying the refractive index to industrial applications, contact Electron Machine Corporation by calling 352-669-3101 or by visiting

Process Refractometers for Black Liquor and Green Liquor Processes in Pulp and Paper

Black liquor refractometer
The only thing that a pulp and paper plant doesn't reuse is the "shade the building casts". When you consider reuse of energy and byproducts, the processes used in the production of pulp and paper are very efficient. Efficiency is costly however, because of the very hostile environments and demanding operating conditions endured by the plant's process equipment.

As an example, the "Kraft Process" (also known as the sulfate process) is the method of converting wood chips into pulp and cellulose fibers. The wood chips are mixed with sodium hydroxide and sodium sulfate, then soaked, cooked and processed.

A very fundamental explanation of the Kraft Process:

Wood chips are soaked and processed as "white liquor" in a mixture of sodium hydroxide and sodium sulphates. After impregnating the wood chips with white liquor, they are then cooked in digesters to break wood into cellulose. The solid pulp is then separated and the rest of the fluid is called the "black liquor". Black liquor is also processed for the removal of solids and chemicals to be reused during pulping. One of the final by-products is "green liquor" which contains both sodium carbonate and sodium sulfide and is then reacted into more white liquor with the addition of lime. All of these processes expose instruments, processing equipment, piping and valves to very harsh environments and chemicals. 

Electron Machine Corporation, a manufacturer of extremely robust process refractometers, has for over 40 years, been actively perfecting the use of refractometers for the measurement of green and black liquor density. 

Scaling of the sensor head: A key issue for keeping the system operational.

heated high-pressure cleaning system
 MPR E-Scan and heated high-pressure cleaning system.
The problem of scaling in black liquor and green liquor applications is a major concern. It results in an optical coating on the sensor head of the refractometer the deteriorates performance. This scaling needs to be kept in-check in order to permit an acceptable duration of online measurement. With a means of effective removal at the time the the coating happens, the refractometer accuracy can maintained with minimum maintenance and downtime.

Electron Machine's decades of effort and experience in the pulp and paper industry led to the development of their MPR E-Scan refractometer in tandem with their heated high-pressure cleaning system. The resulting combination ensures efficient optical coating removal  and maintenance minimization so as to ensure a reliable measurement source for automatic online control.

For more information about the use of process refractometers in pulp and paper production contact Electron Machine Corporation by calling 352-669-3101 or visit their website at

Accurate Green Liquor Density Control with Reduced Maintenance

HPC-2 High Pressure Cleaner

In pulp and paper processing, the term "green liquor" refers to a by-product of kraft pulping. It is the dissolved concentration of sodium sulfide, sodium carbonate, and other compounds in solution from the recovery boiler. The measurement and control of its concentration is important in the pulp and paper production cycle. 

Inline refractometers are used to provide continuous density measurement of green liquor in the pulp mill. A major issue in handling green liquor is scale build up and the resulting optical coating on the refractometer sensing head. If scale build-up is controlled for an acceptable amount of time during processing, the maximum accuracy of the refractometer will be achieved and the overall quality of the pulping process is supported. Understandably, it makes great sense that a system of measuring scale potential and a means to automatically clean the sensing head should be implemented.

The Electron Machine MPR EScan is used to measure the green liquor dissolved density, or TTA, at two stages in the process: after the green liquor dissolving tank and after the green liquor clarifier. The inline measurement, with the refractometer sensing head installed directly in the main process lines, allows real-time control of green liquor dilution to meet target TTA set-points. The measurement is also used to indicate (and prevent) excessive green liquor density and the resulting dangerous impending crystallization within the dissolving tank, and lower the potential for scaling.

Scaling issues, and therefore accuracy problems, are further reduced with the use of ancillary inline cleaning systems that use pressurized water, heated to the process temperature, to effectively clean the refractometer optical components. The Electron Machine HPC-2 High Pressure Cleaner is one example of a completely integrated system.

The compound result of using a refractometer to keep green liquor density within optimal levels, plus an inline cleaning system, provides an excellent payback both quality control and also with associated maintenance requirements.

Using a Spool Adapter with Your Inline Process Refractometer

Spool Adapter
Two versions of inline refractometer adapters.
Inline refractometers use process adapters as the mechanical connection between the refractometer sensing head and the process piping. The adapter, also referred to as a "spool piece", is designed specifically to accommodate the pipe size and application.

On applications where pipe sizes are 2" or larger, the use of a refractometer sensing head spool adapter is suggested. This ancillary piece of hardware provides a mounting point for the sensing head between two flanges directly in the process piping.

The spool adapter positions the sensing head so that it measures from the center of the process flow. The spool adapter design includes an internal deflector and a 5 degree (angular) sensing head mounting connection. The deflector and angled mounting connection reduces sensor head coating issues from the process media. A steam purge tube connection is standardly included to accommodate steam/fluid cleaning.

Spool Adapter
Spool adapter with sensing
head mounted.
Spool adapters recommended mounting orientation is horizontal, generally placed in a horizontal segment of process piping. Vertical mounting is also acceptable, as long as the process flow is in an upward direction.

Spool Adapter
Spool adapter with hand
cleaning option.
Inline refractometer spool adapters are available with option to facilitate cleaning, service and process protection. Examples are lined adapters, hand cleaner adapters, high pressure cleaner adapters, isolation valves, sanitary connection adapters, and weld-in adapters.

BLRBAC Recommended Good Practice Document: Thermal Oxidation of Waste Streams in Black Liquor Recovery Boilers

The black liquor recovery boiler presents problems of operation and safety that far exceed those of the conventional power boiler or other forms of combustion equipment that can be used for the thermal oxidation of waste streams. The recovery boiler is primarily a chemical recovery process unit in which organic materials in the black liquor are burned while the oxidized sulfur compounds of sodium and potassium are reduced and drained as molten smelt from the furnace bottom. At the same time, the heat released is used for generation of steam for power and process.

This document is intended to address concerns of the industry relating to safe thermal oxidation of waste streams in recovery boilers. “Waste streams” for this document are produced in the pulping process. The major waste stream is noncondensible gases (NCG), which are gases that contain reduced sulfur compounds from the digester and evaporator operations and are a source of odor.

The following list is representative of the pulping process waste streams that are addressed:
  • Dilute Noncondensible Gas (DNCG)
  • Concentrated Noncondensible Gas (CNCG)
  • Stripper Off Gas (SOG)
  • Chip Bin Noncondensible Gas (CBNCG)
  • Dissolving Tank Vent Gas (DTVG)
  • Soap
  • Methanol
  • Turpentine
  • Tall Oil
  • Spent Acid
  • Secondary Sludge