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

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.

 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 https://electronmachine.com.

Accurate Green Liquor Density Control with Reduced Maintenance

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

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 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 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.

Using the Refractive Index for Better Product Quality and Safety Since 1952

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

DOWNLOAD THE FULL BLRBAC DOCUMENT HERE

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Process Refractometers for Instant Coffee Production

The morning alarm rings and you slowly rise for your daily routine.  You can’t wait to get the first taste of your day: Coffee!  One of the first things millions of people do worldwide to start their day is enjoy a nice hot cup of coffee.  Some people brew their own fresh coffee, some buy it ready made at their local convenience store or coffee shop, while others turn to their favorite brand of instant coffee (just add hot water, stir and it’s ready).

Approximately one third of all coffee consumed worldwide is instant coffee.  That number is lower in the United States, but other countries such as Great Britain and Japan love the stuff!  Instant coffee differs from the fresh ground bean version because it has already been brewed before at the factory.  The raw beans are cooked to perfection by the manufacturer.  They are then ground and brewed to very specific taste standards.  After the perfect brew is made, it is freeze dried and ground into tiny morsels just begging for some hot water to release their flavor again. 

The consistency and quality of the instant coffee that comes from each brewed batch is of vital
importance to the manufacturer.  If the end product is not consistent with the customers’ taste standards, then the brand will lose customers to other manufacturers who have a better, more consistent, brew.  It is during the brewing process where the inline refractometer plays a huge role in quality control.

Process refractometer sensor.

In the production of instant coffee, as large batches of coffee are brewed, process refractometers are used to monitor concentrations in evaporation procedures. The process refractometers are used to measure the amount of total dissolved solids (TDS), which refers to the amount of the soluble flavor material from the coffee bean that is extracted as a part of the brewing process. Coffee grounds are made up of about 70% non-soluble material and about 30% of soluble compounds. These soluble compounds are responsible for the coffee's taste. For a delicious instant coffee time and time again for the customer, the manufacturer must keep tight TDS tolerances on their batches of brew.  If the TDS measurement varies too much in each brewed batch, the end product will be inconsistent. This will lead to customer dissatisfaction, and ultimately loss of sales.

So the next time you enjoy a nice hot cup of instant coffee...thank the refractometer for helping maintain its’ deliciously consistent taste!

Electron Machine Corporation manufactures inline, process refractometers for large scale food and beverage production applications.

https://electronmachine.com
352-669-3101

The Important Role of the Inline Refractometer in Juice and Beverage Production

Every time a consumer purchases a beverage that they enjoy drinking again and again, it is because they love the taste of their favorite drink.  Why do they love it?  Because they have grown to trust that the taste they expect is always the same!  They continue to purchase their favorite drink because it is dependable, reliable, and delicious for them every time!

The consumer gets this feeling because of the consistency of product. The consistency is a function of production processes on the part of the manufacturer. Many drinks and beverages have a certain amount of sugar added for optimal taste.  If the process used to mix the sweetener into the drink deviates, even in the slightest, then product consistency will suffer and so will consumer satisfaction.

Enter the process refractometer.  With its precisely calibrated refractive index set to the exact parameters specified by the manufacturer, the quality and consistency of each and every product batch will fall within the acceptable quality control range.  Any deviation from the "sweetness" settings (degrees Brix) are immediately detected by the inline refractometer, and can be quickly corrected by automated signals sent to a final control element and eliminate the deviation. This ensures a quality product for consumers time in and time out, as well as keeping costly losses due to defective batches at a minimum.

Another area in beverage production where inline refractometers are used is in the container and piping sanitization processes. Each producer must keep their process components cleaned and sanitized to industry and government standards. The beverage manufacturer needs to ensure container cleanliness prior to filling, and also guarantee proper flushing of the process piping during product changeover. The cleaning process is regularly done with some aggressive chemicals, namely hydrogen peroxide and sodium hydroxide.  Inline refractometers are used to ensure the precise concentration of theses two cleaning agents. By using the specific refractive index of each chemical, a process refractometer can control the optimal amount for the cleansing processes, again ensuring quality and consistency on the part of the manufacturer, while offering peace of mind that the process components are cleaned and sanitized to exact industry and government standards.

Process refractometers proved an extremely important role in the production of juices and beverages in both the product consistency, and also the safety and cleanliness of the production process.

For more information, contact Electron Machine Corporation by calling 352-669-3101 or visit their web site at https://electronmachine.com.