Safeguarding the Pulp Industry: The Role of BLRBAC

The Black Liquor Recovery Boiler Advisory Committee (BLRBAC) ensures safety within the pulp and paper industry. Formed in 1962, BLRBAC focuses on improving the safety, reliability, and operation of black liquor recovery boilers, essential systems used in pulp production. These boilers recover chemicals and energy from black liquor, a byproduct of the pulping process, while also generating steam for energy. However, the high pressures, temperatures, and chemical processes involved make recovery boilers inherently dangerous. BLRBAC was established to address these risks and prevent catastrophic incidents.

BLRBAC's inception was a direct response to the perilous nature of black liquor recovery boilers, which have a troubling history of severe accidents, including explosions caused by unsafe operating conditions. One of the most serious risks is a smelt-water explosion, a violent detonation triggered by water leaking into the smelt pool. These hazards compelled the pulp and paper industry to acknowledge the necessity of a specialized body to develop safety standards for designing, operating, and maintaining recovery boilers. In answer to this urgent need, BLRBAC was formed, focusing on sharing expertise, research, and guidelines to promote safe and efficient operations.

The committee fosters collaboration across the pulp and paper industry by providing a platform where industry representatives, equipment manufacturers, insurers, and regulatory agencies can share experiences and develop solutions to common challenges. By encouraging open communication, BLRBAC helps establish industry-wide safety standards that reduce risks and prevent accidents. The committee ensures its guidelines reach industry professionals through regular meetings and publications, helping maintain safe and efficient recovery boiler operations.

BLRBAC draws its members from a wide array of sectors, including pulp and paper companies, boiler manufacturers, suppliers, insurers, and engineering firms. This diverse membership base provides a broad range of perspectives and expertise, enabling BLRBAC to tackle complex safety challenges comprehensively. The committee's bi-annual meetings concentrate on recent developments, case studies, and updates to technical guidelines based on the latest industry insights, making it a key driver of safety and reliability improvements in recovery boiler operations.

Electron Machine Corporation has shown a deep commitment to BLRBAC, consistently supporting the committee's safety mission. As a leading provider of process instrumentation, Electron Machine understands the critical importance of safe operations in black liquor recovery boilers. The company actively contributes technical expertise and innovative solutions that align with BLRBAC's goal of reducing risks and preventing accidents.

Electron Machine's involvement in BLRBAC extends beyond participation. The company engages directly in the committee's initiatives, sharing valuable insights from its extensive experience in process measurement and control. By remaining closely involved with BLRBAC's efforts, Electron Machine ensures its products meet the highest safety standards and helps foster a culture of safety throughout the industry.

Through its membership in BLRBAC, Electron Machine actively collaborates with industry leaders, including pulp and paper manufacturers, boiler designers, and safety engineers. This engagement keeps the company at the forefront of technological advancements and safety practices, allowing it to continuously develop solutions that meet the evolving demands of recovery boiler operations. Electron Machine's active role in BLRBAC underscores its dedication to advancing safety and efficiency in the pulp and paper industry, reassuring the audience about the company's commitment to safety.

Electron Machine Corporation
https://electronmachine.com
+1 352-669-3101

Electron Machine Corporation: Pioneering Industrial Refractometers

The refractometer, an instrument that measures the refractive index of a substance, has long been a staple in labs across various scientific fields. However, the transition of this tool from its conventional lab-bound limitations to vast industrial applications was driven mainly by the innovative efforts of the Electron Machine Corporation under the leadership of its founder, Carl Vossberg, Jr.

Electron Machine Corporation takes immense pride in its distinguished history and entrenched presence in the electronic instrumentation industry. Carl Vossberg, Jr., the brain behind Electron Machine Corporation, pursued electronics at City College of New York, Columbia University, and the Massachusetts Institute of Technology. During WWII, he collaborated with the U.S. Office of Strategic Service (now the CIA), contributing to creating remote radio transponders, artillery tracking systems, weapon fire detection controllers, and video transmission.

Post-war, Carl Vossberg Jr. endeavored to harness his electronics expertise for industrial purposes. He established Electron Machine Corporation in 1946, initially operating out of a radiator repair shop in New York. The company birthed and licensed innovative instruments, such as the first commercial x-ray thickness gauge, optical cable diameter gauges, and an industrial process control computer.

By 1952, Electron Machine Corporation relocated to Umatilla, Florida, where it operates today. Recognizing a gap in the burgeoning concentrated Citrus industry, the company developed the first in-line process refractometer. 

Subsequently, they constructed a 25,000-square-foot manufacturing facility, maintaining their roots in Umatilla. In 1977, the mantle passed to Carl Vossberg III, who amplified the refractometer's applications worldwide across the food, chemical, and pulp/paper sectors. With the integration of microprocessor technology, the instruments saw marked enhancements in accuracy and reliability. 

Today, under continued third-generation C.A. Vossberg's leadership, the corporation thrives as a vertically integrated manufacturer, ensuring unparalleled service and support by efficiently controlling its manufacturing timeline, leading innovation, maintaining high-quality standards, and fostering partnerships for community engagement.

The company achieves exceptional quality control by integrating contemporary technology and methodologies with foundational designs. Modern advancements at the company encompass in-house microprocessor and DSP software design, surface-mount PC card design and assembly, 3D CAD/CAM design, CNC machining, and MIG/TIG welding. Moreover, the founder's pioneering spirit remains alive and influential, guiding the company's ongoing research and product development endeavors.

Electron Machine Corporation
https://electronmachine.com
+1 352-669-3101

Process Refractometers in The Kraft Pulping Process

Process refractometers are optical instruments that measure the refractive index of a substance to determine its concentration. They are widely used in the pulp and paper industry, particularly in the Kraft pulping process, to measure the concentration of essential chemicals in white, green, brown and black liquors.

The kraft process, which employs sodium hydroxide (NaOH) and sodium sulfide (Na2S) to convert wood into pulp, is the predominant pulping technique in the pulp and paper sector. This method is responsible for an annual production of approximately 130 million tons of kraft pulp worldwide, contributing to two-thirds of global virgin pulp output and over 90% of chemical pulp. Kraft pulp's superior strength, the process's compatibility with nearly all types of softwood and hardwood, and its economic benefits stemming from a high chemical recovery efficiency of about 97% make the kraft process more favorable than alternative pulping methods.

Process refractometers apply in the following steps of the Kraft pulping process:

• Green Liquor Control: After burning the black liquor, the resulting green liquor contains sodium carbonate (Na2CO3) and sodium sulfide (Na2S). Refractometers measure the green liquor's concentration, which helps optimize the causticizing process. This process involves converting sodium carbonate to sodium hydroxide by adding lime (calcium oxide, CaO). Accurate measurement of green liquor concentration ensures the right amount of lime is added, thus optimizing the efficiency of the causticizing process and reducing waste.
• Brown Liquor Control: After the causticizing process, the remaining liquor, called "brown liquor," primarily contains sodium hydroxide (NaOH) and sodium sulfide (Na2S). The concentration of brown liquor is critical for achieving the desired pulp quality and yield. Refractometers help maintain the correct concentration of brown liquor, ensuring consistent pulp quality and minimizing chemical waste.
• Black Liquor Evaporation: Black liquor is concentrated through evaporation to increase its solids content before being burned in the recovery boiler. Process refractometers monitor the concentration of the black liquor, ensuring optimal evaporation rates and preventing potential issues in the recovery boiler.
• White Liquor Quality Control: Refractometers can also be used to monitor the concentration of white liquor, helping maintain the desired alkalinity and sulfide levels, directly affecting the cooking process and pulp quality.
• Recirculation and Monitoring: Process refractometers can be installed at various points in the Kraft pulping process, such as in recirculation lines, to monitor liquor concentrations continuously and adjust process parameters accordingly.

Process refractometers play a crucial role in Kraft pulping by monitoring and controlling the concentrations of green, brown, and black liquors. Their accurate measurements ensure the efficient use of chemicals, minimize waste and help maintain consistent pulp quality.

Electron Machine Corp.

https://electronmachine.com

+1 352-669-3101

The Crucial Role of Inline Process Refractometers in Manufacturing Industries

Industrial refractometers are an indispensable component of process automation because they contribute to maintaining product quality and uniformity, reducing waste, and enhancing output. A substance's refractive index can be determined using a refractometer, which assesses the degree to which a sample causes light to bend as it travels through the process media. This measurement provides helpful information regarding the composition and concentration of a solution, both of which are essential in a wide variety of industrial processes. 

Industries That Commonly Use Inline Process Refractometers:

• Inline process refractometers are used in pulp and paper manufacturing to determine the percent of dissolved solids present during various stages of the production process. These phases include the pulping process, the bleaching process, and the paper coating process. 
• Inline process refractometers are commonly used in the food and beverage sector to determine the percentage of sugar occurring in various goods like juices, jams, and other condiments. This measurement contributes to ensuring that the products have a consistent flavor and texture across the line and meet all regulatory criteria. 
• In the pharmaceutical sector, process refractometers measure the concentration of active pharmaceutical substances, an essential step in ensuring the product is effective and safe. 
• In the production of semiconductors, inline process refractometers measure the concentration of chemical solutions utilized in various production processes. These processes include cleaning, etching, and chemical mechanical planarization. 
• Process refractometers assist in producing industrial chemicals to measure the concentration of dissolved solids such as salts, acids, and other compounds at various points throughout the production process. 

Industrial refractometers offer real-time, precise, and dependable measurements by automating the process of measuring refractive index, thus eliminating the need for manual testing. This automation minimizes errors, enhances process efficiency, and reduces labor costs that result from manual testing. Additionally, automated refractometers supply data to distributed control systems and PLCs, enabling continuous monitoring and regulation of essential process parameters.

In general, industrial refractometers play an essential part in the automation of processes. They contribute to the maintenance of product quality and consistency, as well as to the enhancement of efficiency and productivity, as well as to the reduction of waste and expenses. As automation technology progresses, refractometers and other process monitoring devices may take on an even more significant role in industrial settings.

Electron Machine Corporation
https://electronmachine.com
+1 352-669-3101

Inline Process Refractometers for Industry

Refractometry is the ideal method for efficiently, reliably, and accurately determining substance concentration, identification, or purity. Inline process refractometers are especially helpful as they supplement laboratory research and contribute to product improvement. These process analyzers deliver results within fractions of a second, allowing real-time monitoring and automatic control of processes.

Process refractometers offer the end-user a tool that can be relied upon consistently. They provide a consistent final product, which is essential for various reasons that vary depending on the business that utilizes this equipment. In the pulp and paper industry, managing the process to their desired level enables them to enhance and simplify the whole Kraft process, allowing them to operate at optimum energy efficiency, which is essential given the competitive global market. 

The same applies to chemical, food, dairy, and sugar-producing businesses. However, quality control is very crucial. Creating and sustaining brand loyalty is vital, and quality control guarantees quality. Product uniformity each time your client's purchase will help you earn and maintain market share. Not to mention saving money via waste reduction.

The benefits of using inline refractometers are apparent. Manual sampling and laboratory analysis are time-consuming and labor-intensive, making them less efficient and reproducible. The inline process refractometer is the more efficient and dependable option. These instruments provide real-time, inline continuous concentration monitoring and cross-contamination prevention. Furthermore, operators may utilize their time to do other vital tasks, allowing for further time savings and quality improvements.

Electron Machine Corporation
https://electronmachine.com
+1 352-669-3101

The MPR E-Scan™

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.). This reading may be used as an error indicator or part of a complete process control system. A high-resolution color display and a 4-20mA output is standard. HART® protocol, RS-232, and RS-422 outputs are available. Each sensing head is custom tailored and calibrated specifically for the desired process application to ensure the most accurate and useful reading. 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.

Learn more at https://electronmachine.com or call 352-669-3101.

Inline Process Refractometers for Pulp & Paper Mill Applications

Approximately 50 years ago, the Electron Machine Corporation became the first company to employ refractometers to precisely quantify the dissolved particles in black liquor. Our extensive experience with this application has resulted in several design characteristics specifically tailored to process measurement challenges in this demanding environment. For decades, the paper industry has also relied on Electron Machine refractometers to correctly measure green liquor solids in pulp and paper manufacturing.

Electron Machine

352-669-3101

https://electronmachine.com

Green Liquor Process Management with Inline Refractometers

Green liquor is the dissolved concentrations of sodium sulfide, sodium carbonate, and other substances from the paper-making process's recovery boiler. Measuring its density is an essential aspect of paper production quality. 

The Electron Machine MPR EScan is used to measure the green liquor dissolved density, or TTA, at two different points in the process: after the green liquor dissolving tank and after the green liquor clarifier. With the refractometer sensing head positioned directly in the primary process lines, inline measurement enables real-time management of green liquor dilution to meet target TTA set-points. Excessive green liquid density and the accompanying harmful imminent crystallization within the dissolving tank are also indicated (and prevented) by the measurement. 

One considerable challenge is sensor head scaling associated with green liquor. An optical coating forms on the refractometer sensing head. The coating must be dealt with efficiently and quickly to maintain the accuracy and with minimum maintenance. This is key for the refractometer's ability to provide an acceptable measurement cycle and duration. The maintenance necessary to keep the cleaning system running efficiently is challenging. 

Controlling scaling is optimal when the variance of green liquor solids is reduced by automatically adjusting weak-wash dilution with the MPR E-Scan refractometer. Additionally, pressurized water, heated to the process temperature, rinses the refractometer optical components effectively, resulting in a further scaling reduction. The end outcome is advantageous for both control and acceptable maintenance scheduling. 

By limiting thermal changes, minimizing maintenance, and providing a dependable measurement source for automatic inline control, refractometers with accompanying heated high-pressure water cleaning systems deliver excellent results in improving green liquor processing.

Visit www.electronmachine.com or contact 352-669-3101 for more information.

Inline Process Refractometers Used in Industry

Inline process refractometers are used in a wide variety of industrial and commercial applications including the measurement of the sugar content of food and beverages, monitoring the purity and concentration of ingredients in pharmaceuticals, analyzing the constituents in chemical used in pulp and paper processing, and purity control and concentration measurement of raw materials in the chemical industry.

Inline process refractometers provide a very reliable and accurate real time measurement, which is ideal for process loop optimization and control. With In-line process refractometers, product quality and batch times are more closely controlled, reducing costs as a result.

The Electron Machine Corporation has been designing and manufacturing in-line process refractometers since the early 1960s, with a focus on providing simple, rugged, and reliable instruments that provide value over time, with accurate measurement, minimal maintenance, and long service life. They are the pioneer in developing the industrial use of refractive index for safe, reliable, and accurate process measurement and control.

Electron Machine Corporation
https://electronmachine.com
352-669-3101

Process Refractometers

Process refractometers are used in a wide variety of industrial and commercial applications including the measurement of the sugar content of food and beverages, monitoring the purity and concentration of ingredients in pharmaceuticals, analyzing the constituents in petroleum oil, and purity control and concentration measurement of raw materials in the chemical industry.

PROCESS REFRACTOMETERS FOR THE FOOD AND BEVERAGE INDUSTRY

• Quality control and purity determination of feedstock and end products.
• Determination of sugar concentration (Brix).
• Determination of the alcohol concentration in beer, wine and spirits.
• Quality control of milk-based products

Substances Monitored

• Dairy products, jams and jellies, tomato products, fruit juices, beer, wine, spirits.

PROCESS REFRACTOMETERS FOR THE CHEMICAL INDUSTRY

• Baseline development of concentrations in research and development.
• Quality control and purity determination of feedstock and end products.
• Chemical process monitoring during production.

Substances Monitored

• Hydrocarbons, organic solvents, alcohols, salt solutions, acids, bases, stains, paints and varnishes, industrial oils, resins, glue, polymers, silicones, hydrochloric acid applications, sulphuric acid applications, boiler cleaning chemicals.

PROCESS REFRACTOMETERS FOR THE PULP AND PAPER  INDUSTRY

• Black liquor concentration and quality.
• Green liquor concentration and quality.
• Boiler cleaning chemicals.

Substances Monitored

• Green liquor, black liquor, boiler cleaning chemicals, red liquor, white liquor, tall oil, and resin.

For more information, contact Electron Machine Corporation.

Industrial Refractometers and Green Liquor Scale Mitigation

Green liquor, a by-product of the kraft process, is the dissolved concentration of sodium sulfide, sodium carbonate, and other compounds in solution. Keeping track of its component concentration is important to the pulp processing cycle. Green liquor scaling, which includes calcite, sodium aluminosilicates, and pirssonite,  is a problem in most kraft process mills and can cause huge maintenance problems and slow production. Understanding the formation of, and potential ways to control, these formations scale is critical for optimal safety and performance.

Industrial inline process refractometers, such as Electron Machine's MPR E-Scan, are 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 mounted 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.

Refractometer Optical Sensor Cleaning System 

Refractometer operating conditions must be optimized for close monitoring and control of green liquor density. Consideration of scale and coating build-up on the optical sensor on the refractometer sensing head is a primary area of concern. A clean sensing head will allow maximum accuracy of the refractometer,  maintaining tight density control, minimize scaling, and increasing kraft process quality.

With overall quality and safety in mind, the use of a refractometer sensing head cleaning system is compulsory. The use of ancillary inline cleaning systems, such as Electron Machine's HPC-2 High Pressure Cleaner, that use pressurized water heated to the process temperature, will clean the refractometer optical components and therefore mitigate scaling issues and the related quality, safety, and production problems in the kraft process.

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.

Throwback Thursday - 1972 "Instrumentation Study - Black Liquor Solids Content" by the The Institute of Paper Chemistry

For all you Pulp & Paper historians out there, here's an "oldie but goodie" from the Electron Machine archives.

In 1972 The Institute of Paper Chemistry wrote a paper titled "Instrumentation Study - Black Liquor Solids Content" detailing a comparison between an Electron Machine Corporation refractometer and an NUS Corporation sonic velocimeter and their respective capability of measuring black liquor solids. Below is the document to view online, or you can download your own copy here.

Instrumentation Study: Black Liquor Solids Content - Electron Machine Corporation Refractometer vs NUS Corporation Sonic Velocimeter from Electron Machine Corporation

The Three Major Causes of Refractometer Trouble in Black Liquor Recovery Boilers

Pulp and paper mill.

The three major causes of refractometer trouble or failure in black liquor recovery boilers are:

1. Loss of cooling water and its effect on the sensing head.
2. Lack of reliability of the prism wash.
3. Condensation in the sensing head.

These may not apply to all refractometers due to differences in construction and circuitry.

Cooling Water Loss

It is of vital importance that the loss of cooling water be detected. This may be done through a temperature sensing element or flow monitor which shuts down the refractometer involved.

Damage to the sensing element of a refractometer does not occur instantaneously, but it is essential that the system detect abnormal temperatures due to cooling water loss, flow blockage, etc., and that the cooling water be promptly restored.

The individual refractometer manufacturer’s instruction and maintenance manuals shall be consulted with reference to: potential damage to the sensing element; identification of a damaged element; how and when to replace a damaged element.

Prism Wash

The time interval between prism washes may vary with the black liquor composition. It is recommended that the minimum wash period be 7-10 seconds of wash every 20 minutes. Short duration washes at more frequent intervals are more effective than long washes at long intervals. Ideally, steam pressure for prism washing should be 35 psig above the black liquor pressure, plus the pressure required to open the protective check valve.

Awareness must be maintained of the effect of changes to the prism wash programming variables. Various refractometer systems have the capability to adjust: condensate drain time, steam on time, recovery time and interval between wash time. It may be possible to configure the system to have the total time that both refractometers are in their wash cycle represent a significant percentage of operating time. If one refractometer is out of service for repairs and the remaining refractometer is in prism wash, black liquor solids are not being monitored. Prism wash should be minimized to that needed to maintain the system.

If high pressure steam is used, it may abrade the prism. If only high pressure steam is available, a reducing valve shall be used.

The refractometer prism must have a clear polished optical surface, and if it becomes abraded, it must be replaced.

If the prism wash system has not operated properly and the prism becomes coated, it must be removed and properly cleaned.

Condensation in Sensing Head

Condensate may build up in the refractometer sensing head and if this occurs, the instrument operation will be erratic.

The procedure for determining this condition and for the elimination of excessive moisture in the sensing head is not the same for all refractometers. The manufacturer’s instruction and maintenance manuals shall be consulted and followed carefully.

Reprinted from "Recommended Good Practice: Safe Firing of Black Liquor in Black Liquor Recovery Boilers" courtesy of the Black Liquor Recovery Boiler Advisory Committee.

Image by AlexiusHoratius [CC BY-SA 3.0  (https://creativecommons.org/licenses/by-sa/3.0)], from Wikimedia Commons

Applying Refractometers to the On-line Measurement of Green Liquor Density

A presentation to the Black Liquor Recovery Boiler Advisory Committee (BLRBAC) by C.A. Vossberg, President of Electron Machine Corporation.

Download the PDF version of "Applying Refractometers to the On-line Measurement of Green Liquor Density" from this link.

Applying Refractometers to the On-line Measurement of Green Liquor Density from Electron Machine Corporation

Black Liquor Recovery Boilers

Recovery Boiler (courtesy of Wikipedia)

Article courtesy of Electron Machine Corporation

“Black liquor” is a term used for the waste products that result from the pulping process. The black liquor recovery boiler (BLRB) allows for the chemicals in the waste products to be reclaimed via combustion. These reclaimed chemicals are then utilized to both meet steam demands in the process and to generate electricity.

Modern day BLRBs are designed similarly to industrial boilers, typically as two drum designs, for operating pressure under 900 psi, or single drum designs, for operating pressure over 900 psi. The combustion gases utilized by the boilers can be sticky, so the BLRB furnaces are taller than their utility or industrial watertube counterparts. The amount of pulp producible by a particular mill directly correlates to the size of the BLRB. Small BLRBs process about 750,000 pounds of dry solids per day, and larger BLRBs process about six million pounds of dry solids per day. Precise attention and vigilant maintenance are required in order to maximize investment return for each particular boiler.

Black Liquor

In order to ensure stabilization of combustion, BLRBs are equipped with auxiliary burners which raise boiler temperature for the combustion process. The firing of the black liquor will eventually become self-sufficient. Combusting the black liquor allows for sulfur compounds used in the pulping process to be reduced to sulfide while inorganic chemicals essential to the process are melted down for reuse. The furnace vaporizes the black liquor as the liquor is sprayed into the furnace. Extra water is vaporized, and some of the combustion takes place as the black liquor falls to the furnace’s floor. The resulting molten smelt flows through spouts, which are operantly cooled via water, to a smelt dissolving tank.

A particular risk of the BLRB process stems from the relationship between molten smelt and water. The pool of molten smelt that accumulates as a result of the reclamation process needs to be kept separate from water, because water and molten material mixing at high temperatures can result in a smelt-water explosion. These explosions can occur when black liquor water content is greater than 42% of the mixture. Additionally, there are numerous ways water can enter the process – as condensation from the soot blower, a faulty steam coil heater, wash hoses – so controller vigilance is absolutely key to explosion prevention.

The Black Liquor Recovery Board Advisory Committee has recently introduced an emergency shutdown procedure, where an emergency evacuation alarm signals as soon as suspected water enters the BLRB furnace. The operator, with corresponding training, shuts down all fuel flow and minimizes combustion until all but a minimal amount of water is drained rom the BLRB. Annual inspections of BLRBs mandate the testing of all pressure parts and safety systems, because utmost care must be assured in preventing risk of system damage or operator harm when dealing with BLRB processes.

Quality and Process Optimization with Inline Refractometers

Process refractometer
in plant.

Process refractometer
(Electron Machine Corp.)

Refractometry is a technology used to quickly, reliably, and very accurately identify a sample and determine the concentration and purity levels. This is done be taking a sample and measuring the refractive index and temperature of the media.

Process refractometers are used for monitoring and controlling process variables in the flowing process media (liquid) . These instruments are used for continual, extremely accurate, real-time substance identification. Through identifying critical factors such as the concentration and purity, manufacturer's can gain tight control over quality can consistency of product. Applications for process refractometers are found in commercial food & beverage, chemical, pulp & paper, and pharmaceutical industries. All share similar processes lines where process refractometry provides real-time, high value information about the product at critical points. These shared processes are:

Process refractometers are used
for food and beverage production.

Concentration
The measurement of concentrations in compounds of organic chemicals, inorganic chemicals, and total dissolve solids are often required for product consistency. Process refractometers can be calibrated to detect a wide range of dilute chemicals and dissolved solids and be an excellent feedback mechanism for these process variables.


Mixing 
Using process refractometers for ingredient mixing to control product quality and production reduces errors and limits variance. Comparing the process media to known reference values, through the use of an inline refractometer, optimizes consistency and maintains quality.


Crystallization

Process refractometers are critical
for making pulp and paper.

Crystallization plays a key role in purification in many chemical processes, ranging from pharmaceutical manufacturing to food processing to liquor processing in pulp & paper production.  Keeping track of concentration levels is essential for the crystallization process and process refractometers provide real time information that allow process optimization.



Cleaning

Process refractometers
have many uses in
chemical production.

Changing product runs through existing lines is a major problem area for quality control. If a process line is used in the production of more than one product, it is important to ensure that no cross-product contamination occurs. To virtually eliminate this concern, process refractometers are used to check in for residual product presence (in real-time), providing assurance that purity levels are their highest.

For more information on industrial process refractometers, contact Electron Machine by visiting https://www.electronmachine.com or call 352-669-3101.

Safe Firing of Black Liquor in Black Liquor Recovery Boilers: Refractometer Black Liquor Solids Measurement System

Recovery Boiler
(Courtesy of Wikipedia)

The following is reprinted from Chapter 4 of the Black Liquor Recovery Boiler Advisory Board (BLRBAC) Recommended Good Practice document titled "Safe Firing of Black Liquor in Black Liquor Recovery Boilers" (April 2016).

Information on the BLRBAC can be found here. The full document, as well as other important information, can be found here.

Refractometer Black Liquor Solids Measurement System

4.1 General

The heart of the system for the safe firing of black liquor is the ability to correctly, accurately and reliably measure the solids in the black liquor stream immediately prior to the black liquor guns.  To accomplish this solids measurement, refractometers have proven to be effective for black liquor recovery boiler service. As new techniques in measuring solids are developed and proven, they can be considered. For the solids measurements, two refractometers in series must be used. When both refractometers are in service, the requirement for an automatic black liquor diversion can be satisfied by either of the following options:

1. If either refractometer reads dissolved solids content 58% or below (62% or below if firing >70% solids per guidelines in 6.4 of this document), an automatic black liquor diversion must take place.  
2. When both refractometers read dissolved solids content 58% or below (62% or below if firing >70% solids per guidelines in 6.4 of this document), an automatic black liquor diversion must take place.  

Either option is satisfactory.

If the instrument readings disagree on the percent solids by 2% absolute value, an audible and visual alarm must be given.

If one refractometer fails, or is removed from service, black liquor diversion must then be controlled by the remaining in-service instrument; and if this remaining instrument reads 58% or below solids, an automatic black liquor diversion must take place (62% or below solids if firing >70% solids per guidelines in 6.4 of this document). Black liquor shall not be fired if neither refractometer is in service.  The refractometers should be part of a specifically integrated system adapted to the black liquor service, and include a system to monitor their operation and indicate trouble or failure of the individual refractometer.  Refractometers used without such a monitoring system can fail unsafe and can give improper and unsafe dissolved solids readings under certain conditions.

4.2 Refractometer Control System Functions

The refractometer control system shall be capable of performing the following functions:

1. Monitor the positive (+) and negative (-) supply voltage of each refractometer independently. The refractometer's supply voltage shall be maintained within the predetermined minimum and maximum limits for safe operation.

2. Monitor the lamp voltage or lamp output of each refractometer independently. The refractometers’ lamp voltage must be within the predetermined minimum and maximum limits for safe operation.

3. Monitor the signal amplitude (if chopper circuit devices are used) of each refractometer independently. Each refractometer's signal amplitude must be maintained within the predetermined minimum and maximum limits for safe operation.

4. Monitor the liquor temperature at each refractometer’s sensing head independently assuring that each refractometer's liquor temperature is within the predetermined minimum and maximum limits for safe operation.

5. Monitor the automatic prism cleaning timer system of each refractometer. The sensor output circuit, prior to the hold circuit, should go negative or adequately decrease during the purge cycle.

6. Monitor the automatic prism cleaning timer system to assure that the purge occurs within the predetermined time.

7. Monitor the cooling water to each refractometer sensing head to assure that cooling water is not lost to a sensing head.

If any of these malfunctions (Items 1 through 7) occur, the following action shall be initiated:

a) An alarm shall be activated, identifying the refractometer and circuit at fault.

b) The refractometer shall be electrically removed from the refractometer control system.

c) The remaining “good” refractometer shall remain in service.

8. Compare the refractometer meter outputs. If a difference of 2% (absolute value) solids or greater exists between refractometer readings, an alarm shall be activated.

9. Performs a black liquor diversion, if one refractometer is removed from service or fails in prism wash, and the remaining refractometer fails or reads a solids of 58% or less.

10. Monitor all cables from the refractometer and the components of the control system. If any cable is cut or removed, an alarm shall be activated.

11. Provide primary alarm or diversion functions by a means other than the refractometer indicating meter’s contacts.

12. Have the capability to allow the manual removal of either refractometer from service retaining the remaining refractometer in full service for diversion purposes.

13. Require a manual reset following a black liquor diversion or malfunction of the refractometer control system.

14. Monitor the position of the sensing head isolation valves. A partially closed or closed valve shall activate an alarm and remove the refractometer from service.

15. Initiate a low solids alarm signal from each refractometer at 60% solids or at 70% solids if firing >70% solids per guidelines in 6.4 of this document.

16. Prohibit the simultaneous washing of the individual refractometers.

17. Require manual restoration of a refractometer which has been removed, either automatically or manually, from service.

18. Have provisions for manual prism washing.

19. Require an automatic switch to single refractometer diversion (for systems set to require both refractometers read low solids to divert – dual refractometer diversion) when one refractometer is in a prism wash cycle. Automatic return to the chosen dual refractometer diversion will occur after completion of the prism wash cycle.

All of the above functions may not apply to all refractometer control systems since some refractometers:

a) Do not utilize cooling water,

b) Have sensing heads that are not affected by liquor temperature, etc.,

c) May have differences in electronic circuitry.

4.3 Refractometer Control System - Controls & Indicators 

The refractometer system shall be equipped with the following controls and indicators:

1. Reset switch.
2. Switch or other means to manually remove either refractometer from service.
3. Visual solids display for each refractometer.
4. Status lights indicating “in service”. “inoperative” and/or “malfunction” for the individual refractometer and status of diversion valve.

4.4 Refractometer Control System - Alarms and Indicators  

The recommended alarms and indicators of the refractometer control system are:

4.5 Installation Requirements

1. The refractometers shall be installed in series.

2. The refractometer sensing heads shall be installed in such a manner that the individual sensing heads can be taken out of service or removed without having to valve off the liquor piping or open bypass valves.

3. All cabinets, wiring, etc., shall be suitable for the atmosphere and service conditions normal to a recovery boiler installation.

4. The refractometer sensing heads shall be installed so that the y are accessible and readily serviceable.

5. The refractometer sensing heads may be installed in any position on a vertical pipe run. On a horizontal run of pipe, the sensing heads must be installed on sides of the pipe. The reason for this is to ensure that the prisms are always covered with liquor.  

6. The electrical power supply to the refractometer control system shall be from a dependable (stable) source.  

7. A dependable supply of cooling water of satisfactory capacity must be provided for refractometers requiring sensing head cooling water.  

8. Dry oil-free instrument air shall be provided to the refractometer sensing heads to prevent and control condensation in the heads.  

9. A steam supply source of sufficient capacity shall be provided to meet flow, and minimum and maximum pressures requirements.  All installation requirements may not apply to all refractometers and refractometer systems.  

4.6 Refractometer Problems 

The three major causes of refractometer trouble or failure are:  

1. Loss of cooling water and its effect on the sensing head.  

2. Lack of reliability of the prism wash.  

3. Condensation in the sensing head.  

These may not apply to all refractometers due to differences in construction and circuitry.  

4.7 Cooling Water Loss  

It is of vital importance that the loss of cooling water be detected. This may be done through a temperature sensing element or flow monitor which shuts down the refractometer involved.  

Damage to the sensing element of a refractometer does not occur instantaneously, but it is essential that the system detect abnormal temperatures due to cooling water loss, flow blockage, etc., and that the cooling water be promptly restored.  

The individual refractometer manufacturer’s instruction and maintenance manuals shall be consulted with reference to: potential damage to the sensing element; identification of a damaged element; how and when to replace a damaged element. 

4.8 Prism Wash  

The time interval between prism washes may vary with the black liquor composition. It is recommended that the minimum wash period be 7-10 seconds of wash every 20 minutes. Short duration washes at more frequent intervals are more effective than long washes at long intervals. Ideally, steam pressure for prism washing should be 35 psig above the black liquor pressure, plus the pressure required to open the protective check valve.

Awareness must be maintained of the effect of changes to the prism wash programming variables. Various refractometer systems have the capability to adjust: condensate drain time, steam on time, recovery time and interval between wash time. It may be possible to configure the system to have the total time that both refractometers are in their wash cycle represent a significant percentage of operating time. If one refractometer is out of service for repairs and the remaining refractometer is in prism wash, black liquor solids are not being monitored. Prism wash should be minimized to that needed to maintain the system.

If high pressure steam is used, it may abrade the prism. If only high pressure steam is available, a reducing valve shall be used.

The refractometer prism must have a clear polished optical surface, and if it becomes abraded, it must be replaced.

If the prism wash system has not operated properly and the prism becomes coated, it must be removed and properly cleaned. 

4.9 Condensation in Sensing Head  

Condensate may build up in the refractometer sensing head and if this occurs, the instrument operation will be erratic.

The procedure for determining this condition and for the elimination of excessive moisture in the sensing head is not the same for all refractometers. The manufacturer’s instruction and maintenance manuals shall be consulted and followed carefully. 

4.10 Refractometer Calibration Standardization (Zero Offset) to Off-Line Test  

A Refractometer Standardization (“zero shifting” or “bias adjustment”) is an adjustment of the refractometer calibration curve to an off-line test to account for un-dissolved solids and/or changes in the black liquor chemistry.  This is normally performed while the instrument is actively measuring black liquor solids.

All refractometers shall be verified against a reliable periodic off-line test. (See Chapter 6 – Off-Line Black Liquor Solids Measurement)

The refractometers shall be standardized:

1.  On initial start-up of the recovery boiler.

2.  At any time it is felt or known that one of the refractometers may be deviating from the known black liquor solids content.

3. Any time there is a 2% difference between refractometers. 

The reading of the refractometers shall be checked against the moisture analyzer or microwave analyzer at two hour intervals (8 hour intervals if firing above 70% solids), and the moisture analyzer or microwave analyzer shall be checked by the TAPPI Standard Method, T650-om-05, weekly.

All refractometer standardization changes shall be entered in the recovery boiler “log book.”   

4.11 Refractometer Calibration  

A Refractometer Calibration involves placing two or more “samples” onto the sensor to generate a refractive index vs. dissolved solids curve.  This is typically performed utilizing calibration oils or electronically (depending on supplier) in a controlled environment, while the sensing head is off of the process line.

Calibration procedures shall be done in a manner that does not affect the system’s ability to automatically perform a black liquor diversion utilizing the remaining (active) in-service refractometer.  Improper procedures, or those that defeat the monitoring system described in Chapter 4, can result in the system failing in an unsafe condition.  Refer to the manufacturer’s appropriate procedures.

If the continuous solids monitor refractometer differs from the off-line test field measurement by more than 2% on an absolute basis, the off-line test results must be confirmed and then if required the continuous monitor refractometer should be standardized and/or recalibrated according to the manufacturer’s recommended procedures.  Repeated errors may indicate a failure of a refractometer component.  Refer to the manufacturer’s recommendations for repair or replacement.

Get to Know Electron Machine Corporation

Electron Machine Corporation, headquartered Umatilla, FL, manufactures industrial, inline, process refractometers. As a vertically-integrated manufacturer, we have complete control over the time it takes to manufacture our instruments providing the highest levels of service and support to our customers. Superb quality control is attained by adapting modern technology and practices to existing designs. These include in-house microprocessor and DSP software design, surface-mount PC card design and assembly, 3D CAD/CAM designing, CNC machining, and MIG/TIG welding. Additionally, our founder's innovative nature is still with us as we continue to research and develop new products.

Learn more about Electron Machine at https://www.electronmachine.com or by calling 352-669-3101.

Bleaching of Pulp in the Paper Making Process

The purpose of the bleaching process is to enhance the physical and optical qualities (whiteness and brightness) of the pulp by removing or decolorizing the lignin. Two approaches are used in the chemical bleaching of pulps. One approach called brightening, uses selective chemicals, such as hydrogen peroxide, that destroy chromatographic groups but do not attack the lignin. Brightening produces a product with a temporary brightness (such as newspaper) that discolors from exposure to sunlight or oxygen. The other approach (true bleaching) seeks to almost totally remove residual lignin by adding oxidizing chemicals to the pulp in varying combinations of sequences, depending on the end use of the product. This creates a longer lasting (sometimes permanent) whiteness, but it weakens the fibers and reduces sheet strength. The most common bleaching and brightening agents are chlorine, chlorine dioxide, hydrogen peroxide and sodium hydroxide.

Typically, the pulp is treated with each chemical in a separate stage. Each stage includes a tower, where the bleaching occurs; a washer, which removes bleaching chemicals and dissolved lignins from the pulp prior to entering the next stage; and a seal tank, which collects the washer effluent to be used as wash water in other stages or to be sewered. Bleaching processes use various combinations of chemical stages called bleaching sequences.

The first stage in the bleaching process is the chlorination stage, whose primary function is to further delignify the pulp. Chlorine reacts with lignin to form compounds that are water-soluble or soluble in an alkaline medium, which aids in delignifying the pulp before it proceeds to the next bleaching stage.

The next stage after chlorination is typically the extraction stage. This stage and the remaining stages serve to bleach and whiten the delignified pulp. The extraction stage removes the chlorinated and oxidized lignin by solubilization in a caustic solution.

Chlorine dioxide is often used in bleaching, either in the chlorination stage (as a substitute for some of the chlorine usage - chlorine dioxide substitution) or as an additional chlorine dioxide stage. Chlorine dioxide has 2.63 times greater oxidizing power (on a pound per pound basis) than chlorine and is used for nearly all high brightness pulps.

The next stage is the actual bleaching stage. Hypochlorite is a true bleaching agent that destroys certain chromophobic groups of lignin. It also attacks the pulp so high cellulose degradation occurs in Kraft pulp. Application of hypochlorite to Kraft pulp is usually used only as an intermediate stage of the sequence or to produce semi-bleached pulps. In the bleach process, residual chlorine must be removed through washing in vacuum washers.

Abstracted from Washington State
Air Toxic Sources and Emission
Estimation Methods