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

Sulfite Pulping

Pulping is the term used for the process which separates wood fibers. Chemical pulping, dissolving the lignin in the wood to create a pulp, is the most commonly used pulping process. Chemical pulping creates higher sheet strength than mechanical pulping; however, yields 40 to 50 percent pulp, where mechanical pulping yields 95 percent pulp.

The two main types of chemical pulping are the more common sulfate pulping (most commonly known as Kraft pulping) and sulfite pulping. Kraft pulping accommodates a variety of tree species, recovers and reuses all pulping chemicals, and creates a paper with a higher sheet strength. Sulfite pulp, however, is easier to bleach, yields more bleached pulp, and is easier to refine for papermaking. The major difference between the two types of chemical pulping is the types of chemicals used to dissolve the lignin.

Sulfite Pulping

The concept of sulfite pulping was created in the United States in 1867, however it was not used in a mill until 1874 by a Swedish chemist who was probably unaware of the U.S. Patent (MacDonald, 277). Sulfite pulping produces a lighter pulp than Kraft pulping. It can be used for newsprint, and when bleached can be used for writing papers and for the manufacture of viscose rayon, acetate filaments and films, and cellophane.

Description of Process 

Sulfite pulping follows many of the same steps as Kraft pulping. The major difference in sulfite pulping is that the digester “cooks” with a mixture of H2SO3 (sulfurous acid) and HSO3 ion in the form of calcium, magnesium, sodium, or ammonium bisulfate). The pulp continues on through the same processes as in the Kraft pulping process.

However, the chemicals separated from the pulp in the washers may or may not go into a recovery process. Chemical recovery in sulfite pulping is practiced only if it is economical. If chemical recovery does occur the liquor goes through an evaporator and then to a recovery furnace. Here, smelt is not formed, but ash and SO2 are formed.

Abstracted from Washington State
Air Toxic Sources and Emission
Estimation Methods

MPR E-Scan Deemed RoHS Compliant and Earns CE Marking

Electron Machine Corporation engaged F2 Labs for the technical assessment of the MPR E-Scan using the European standard, EN 50581:2012 Technical documentation for the assessment of electrical and electronic products with respect to the restriction of hazardous substances, to determine compliance with the RoHS Directive 2011/65/EU, and has determined Electron Machine Corporation can claim compliance to the RoHS Directive 2011/65/EU for the subject equipment based upon the supplied documentation.

RoHS stands for Restriction of Hazardous Substances. RoHS, also known as Directive 2002/95/EC, originated in the European Union and restricts the use of specific hazardous materials found in electrical and electronic products.

This certification applies to each portion of the MPR E-Scan (IS), which includes the Console, Cable, Barrier Box, and Sensing Head; along with all components that each of these major subassemblies of the MPR E-Scan contain.

For more information, please contact Electron Machine at 352-669-3101 or by visiting this link.

Paper Manufacturing: Kraft (Sulfate) Pulping

Abstracted from Washington State Air Toxic Sources
and Emission Estimation Methods

Pulping is the term used for the process which separates wood fibers. Chemical pulping, dissolving the lignin in the wood to create a pulp, is the most commonly used pulping process. Chemical pulping creates higher sheet strength than mechanical pulping; however, yields 40 to 50 percent pulp, where mechanical pulping yields 95 percent pulp.

The two main types of chemical pulping are the more common sulfate pulping (most commonly known as Kraft pulping) and sulfite pulping. Kraft pulping accommodates a variety of tree species, recovers and reuses all pulping chemicals, and creates a paper with a higher sheet strength. Sulfite pulp, however, is easier to bleach, yields more bleached pulp, and is easier to refine for papermaking. The major difference between the two types of chemical pulping is the types of chemicals used to dissolve the lignin.

The Kraft process was developed in Germany in 1879 and was first applied to a Swedish mill in 1885. The resulting paper was much stronger than any paper previously made, and therefore the process was named “Kraft”, (German and Swedish for “strength”). Kraft pulping creates dark brown paper which is used for boxes, paper bags, and wrapping paper. Kraft pulp can also be used for writing paper and paperboard when bleached, and for diapers when fluffed.

The three main steps involved in Kraft pulping are:
  1. Digestion: wood chips are cooked
  2. Washing: black liquor is separated from the pulp
  3. Chemical recovery: chemicals are recovered from the black liquor for reuse
Description of Process
  • Digestion 
The first step in pulping wood is to “cook” the wood chips. A digester, heated by steam, “cooks” the wood chips in white liquor (a mix of sodium hydroxide (NaOH) and sodium sulfide (Na2S)) until done. The cooking process dissolves most of the lignin and only some of the hemicellulose , leaving mostly cellulose to hold the fibers together. The digester system may be a batch or a continuous process.

Relief gases are vented continuously from the digester, which helps remove air and other non- condensable gases and reduce the pressure at blow, when the pulp is discharged to the blow tank. After the cooking process, the pulp and black liquor (the chemical mix left after the cooking process) are discharged to a blow tank.

By-products can be recovered from the digestion process. For example, turpentine distills with water out of the blow tank and the evaporators and is separated to be used. The resin acids and fatty acids dissolved from the wood form sodium soaps which are skimmed off the black liquor from storage tanks, evaporators, and black liquor oxidation tanks, and then acidified with sulfuric acid to form tall oil.

Before the washing process, the pulp is usually sent to deknotters, screens used to remove knots (large pieces of fiber not completely broken down in the digester).
  • Brownstock Washing 
Pulp from the blow tank and deknotter is washed with water in a process commonly called brownstock washing. Washing removes weak black liquor from the pulp which is sent to the chemical recovery process. This also prevents contamination during subsequent processing steps. Types of washers used include rotary vacuum washer (most common type of washer), diffusion washers, rotary pressure washers, horizontal belt washers, wash press, and dilution/extraction.

All the washer types use water (fresh or recycled) and are usually placed in series to achieve higher removal efficiency.

The rinsed pulp is screened for oversize particles and then excess water is removed. This is done in a gravity thickener (more commonly known as a decker).
  • Chemical Recovery 
The reason Kraft pulping is economically successful is that the used cooking liquor can be recovered and reused in the chemical recovery process.

The first step in recovering the chemicals from the black liquor is evaporation. This removes excess water from the black liquor and maximizes the fuel value for the recovery furnace.

There are two types of evaporators generally used in the chemical recovery process: direct (DCE) and indirect (NDCE) contact evaporators. Some types of DCE include the multiple-effect evaporator (most common), flash evaporation and thermocompressor evaporation. DCE use heat from direct contact with the recovery furnace flue gases, while NDCE uses indirect contact.

Black liquor oxidation is needed after DCE, but not after NDCE. After DCE, the black liquor is normally oxidized with air to control the sulfide level and prevent the release of odorous compounds. This is done by countercurrently passing the black liquor through an air stream using a porous diffuser, sieve tray tower, packed tower or agitated air sparge. The oxidation reaction converts sodium sulfide to sodium thiosulfate.

After NDCE or black liquor oxidation, the black liquor is then forced through spray nozzles into the recovery furnace, where it is burned providing heat to generate steam. This also conserves the inorganic chemicals, which create a molten smelt on the floor of the furnace.

The molten smelt, composed of sodium sulfide and sodium carbonate, is drained from the recovery furnace hearth through smelt spouts. In a smelt dissolving tank, the smelt is quenched with water, producing green liquor.

Sodium carbonate from the smelt is then converted to sodium hydroxide in the causticizer by adding calcium hydroxide. The calcium carbonate resulting from the reaction precipitates from the solution and is collected and sent to the lime kiln where it is converted to lime (calcium oxide). The calcium oxide is then slaked to produce calcium hydroxide for reuse in the causticizer.

Hybrid-Digital Process Refractometer

hybrid-digital critical angle refractometer
Process refractometers are used for monitoring, controlling, and recording the concentration of dissolved solids in a process media. They accurately measure refractive index and temperature of the process media and provide a visual display in units specific to that process (i.e. Brix, Percent Solids, Dissolved Solids, SGU, R.I.).

The MPR E-Scan is a hybrid-digital critical angle refractometer. It is used to measure the refractive index of process fluids and may be used as an error indicator or an integral part of a complete process control system.

The MPR E-Scan is calibrated and temperature compensated to your process specifications. It is ready for installation and immediate use when received. Calibration procedures are available to change system parameters and allow the refractometer to measure different process fluids.

How It Works: Hybrid-Digital Measurement

hybrid-digital critical angle refractometerEnergy radiated from the LED passes through the prism surface to be reflected off a mirror to the prism-to-process interface. The light reaching this interface intersects the same interface over a series of angles specifically chosen to include the critical angle (Ic) for the process being measured. Light intersect- ing the interface at an angle greater than critical angle is refracted into the solution. Light intersecting the interface at less than critical angle is reflected up out of the prism up to the digital CCD linear array to be scanned.

The resolution of each sensing head is maximized by selecting the angle of the prism for the measurement and temperature range of the process.

MPR E-Scan
MPR E-Scan
The MPR E-Scan refractometer utilizes a hybrid-digital measurement principle. The CCD (charged coupled device) in the sensing head digitally measures the refractive index of the process. Any change in critical angle changes the ratio of light to dark periods. The digital measurement is temperature compensated and converted to a variable voltage by rugged electronic devices in the sensing head. This allows the relatively sensitive micro-processor driven devices to be located in the electronics console where more protection from the process can be provided. The signal is then further enhanced and displayed as a reading in refractive index, Brix, solids, percent, or other measurement unit. This combination of state-of-the-art micro-processors combined with tried-and-true analog components provides a high-level of accuracy along with the rugged dependability required for years of use when installed in harsh industrial environments.

hybrid-digital critical angle refractometer

Isolation Valve Adapter and Safeguard Tool Demonstration

Plant personnel safety is extremely important to Electron Machine. Our Isolation Valve Adapter has a proven track record for safety and reliability for safe removal of our process refactometer sensing heads from a pressurized pipeline. Continuing toward our goal for absolute safety, EMC designed and developed the EMC Safeguard Tool, a device designed to further increase safety should abnormal situations arise when removing a sensing head from the process pipe line. Check out the demonstration below for a full understanding.

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

HART Communication Protocol

HART protocol
(Image courtesy of Lessons in Industrial Instrumentation
and Tony R. Kuphaldt and shared under Creative Commons
4.0 International Public License
).
The Highway Addressable Remote Transducer Protocol, also known as HART, is a communications protocol which ranks high in popularity among industry standards for process measurement and control connectivity. HART combines analog and digital technology to function as an automation protocol. A primary reason for the primacy of HART in the process control industry is the fact that it functions in tandem with the long standing and ubiquitous process industry standard 4-20 mA current loops. The 4-20 mA loops are simple in both construction and functionality, and the HART protocol couples with their technology to maintain communication between controllers and industry devices. PID controllers, SCADA systems, and programmable logic controllers all utilize HART in conjunction with 4-20 mA loops.

HART instruments have the capacity to perform in two main modes of operation: point to point, also known as analog/digital mode, and multi-drop mode. The point to point mode joins digital signals with the aforementioned 4-20 mA current loop in order to serve as signal protocols between the controller and a specific measuring instrument. The polling address of the instrument in question is designated with the number ì0î. A signal specified by the user is designated as the 4-20 mA signal, and then other signals are overlaid on the 4-20 mA signal. A common example is an indication of pressure being sent as a 4-20 mA signal to represent a range of pressures; temperature, another common process control variable, can also be sent digitally using the same wires. In point to point, HART’s digital instrumentation functions as a sort of digital current loop interface, allowing for use over moderate distances.

HART in multi-drop mode differs from point to point. In multi-drop mode, the analog loop current is given a fixed designation of 4 mA and multiple instruments can participate in a single signal loop. Each one of the instruments participating in the signal loop need to have their own unique address.

Since the HART protocol is a standardized process control industry technology, each specific manufacturer using HART is assigned a unique identification number. This allows for devices participating in the HART protocol to be easily identified upon first interaction with the protocol. Thanks to the open protocol nature, HART has experienced successive revisions in order to enhance the performance and capabilities of the system relating to process control. The standardization of “smart” implementation, along with the ability to function with the legacy 4-20 mA technology and consistent development, has made HART a useful and popular component of the process measurement and control industry framework.

Overview of Chemical Recovery Processes in Pulp & Paper Mills

Chemical Recovery Processes in Pulp & Paper Mills
Figure 1
The kraft process is the dominant pulping process in the United States, accounting for approximately 85 percent of all domestic pulp production. The soda pulping process is similar to the kraft process, except that soda pulping is a non-sulfur process. One reason why the kraft process dominates the paper industry is because of the ability of the kraft chemical recovery process to recover approximately 95 percent of the pulping chemicals and at the same time produce energy in the form of steam. Other reasons for the dominance of the kraft process include its ability to handle a wide variety of wood species and the superior strength of its pulp.

The production of kraft and soda paper products from wood can be divided into three process areas:
  1. Pulping of wood chips
  2. Chemical recovery
  3. Product forming (includes bleaching)
Chemical Recovery Processes in Pulp & Paper Mills
Figure 2
The relationship of the chemical recovery cycle to the pulping and product forming processes is shown in Figure 1. Process flow diagrams of the chemical recovery area at kraft and soda pulp mills are shown in Figures 1 and 2, respectively.

The purpose of the chemical recovery cycle is to recover cooking liquor chemicals from spent
cooking liquor. The process involves concentrating black liquor, combusting organic compounds, reducing inorganic compounds, and reconstituting cooking liquor.

Cooking liquor, which is referred to as "white liquor, is an aqueous solution of sodium hydroxide (Na01) and sodium sulfide (Na2S) that is used in the pulping area of the mill. In the pulping process, white liquor is introduced with wood chips into digesters, where the wood chips are "cooked" under pressure. The contents of the digester are then discharged to a blow tank, where the softened chips are disintegrated into fibers or "pulp. The pulp and spent cooking liquor are subsequently separated in a series of brown stock washers: Spent cooking liquor, referred to as "weak black liquor, from the brown stock washers is routed to the chemical recovery area. Weak black liquor is a dilute solution (approximately 12 to 15 percent solids) of wood lignins, organic materials, oxidized inorganic compounds (sodium sulfate (Na2SO4), sodium carbonate (Na2003)), and white liquor (Na2S and Na0H).

In the chemical recovery cycle, weak black liquor is first directed through a series of multiple-effect evaporators (MEE's) to increase the solids content to about 50 percent. The "strong. (or "heavy") black liquor from the MEE's is then either oxidized in the BLO system if it is further concentrated in a DCE or routed directly to a concentrator (NDCE). Oxidation of the black liquor prior to evaporation in a DCE reduces emissions of TRS compounds, which are stripped from the black liquor in the DCE when it contacts hot flue gases from the recovery furnace. The solids content of the black liquor following the final evaporator/concentrator typically averages 65 to 68 percent.

Concentrated black liquor is sprayed into the recovery furnace, where organic compounds are combusted, and the Na2SO4 is reduced to Na2S. The black liquor burned in the recovery furnace has a high energy content (13,500 to 15,400 kilojoules per kilogram (kJ/kg) of dry solids (5,800 to 6,600 British thermal units per pound {Btu/lb} of dry solids)), which is recovered as steam for process requirements, such as cooking wood chips, heating and evaporating black liquor, preheating combustion air, and drying the pulp or paper products. Particulate matter (PM) (primarily Na2SO4) exiting the furnace with the hot flue gases is collected in an electrostatic precipitator (ESP) and added to the black liquor to be fired in the recovery furnace. Additional makeup Na2SO4, or "saltcake," may also be added to the black liquor prior to firing.

Molten inorganic salts, referred to as "smelt," collect in a char bed at the bottom of the furnace. Smelt is drawn off and  dissolved in weak wash water in the SDT to form a solution of carbonate salts called "green liquor," which is primarily Na2S and Na2CO3. Green liquor also contains insoluble unburned carbon and inorganic Impurities, called dregs, which are removed in a series of clarification tanks.

Decanted green liquor is transferred to the causticizing area, where the Na2CO3 is converted to NaOH by the addition of lime (calcium oxide [Ca0]). The green liquor is first transferred to a slaker tank, where Ca0 from the lime kiln reacts with water to form calcium hydroxide (Ca(OH)2). From the slake, liquor flows through a series of agitated tanks, referred to as causticizers, that allow the causticizing reaction to go to completion (i.e., Ca(OH)2 reacts with Na2CO3 to form NaOH and CaCO3).

The causticizing product is then routed to the white liquor clarifier, which removes CaCO3 precipitate, referred to as "lime mud." The lime mud, along with dregs from the green liquor clarifier, is washed in the mud washer to remove the last traces of sodium. The mud from the mud washer is then dried and calcined in a lime kiln to produce "reburned" lime, which is reintroduced to the slaker. The mud washer filtrate, known as weak wash, is used in the SDT to dissolve recovery furnace smelt. The white liquor (NaOH and Na2S) from the clarifier is recycled to the digesters in the pulping area of the mill.

At about 7 percent of kraft mills, neutral sulfite semi-chemical (NSSC) pulping is also practiced. The NSSC process involves pulping wood chips in a solution of sodium sulfite and sodium bicarbonate, followed by mechanical de-fibrating. The NSSC and kraft processes often overlap in the chemical recovery loop, when the spent NSSC liquor, referred to as "pink liquor," is mixed with kraft black liquor and burned in the recovery furnace. In such cases, the NSSC chemicals replace most or all of the makeup chemicals. For Federal regulatory purposes, if the weight percentage of pink liquor solids exceeds 7 percent of the total mixture of solids fired and the sulfidity of the resultant green liquor exceeds 28 percent, the recovery furnace is classified as a "cross-recovery furnace.'" Because the pink liquor adds additional sulfur to the black liquor, TRS emissions from cross recovery furnaces tend to be higher than from straight kraft black liquor recovery furnaces.

Industrial Inline Refractometers for Sucrose, Fructose and Dextrose

The Electron Machine MPR E-Scan is perfectly suited for sugar applications. The refractometer directly measures dissolved solids, which can be easily converted to Brix.

In sugar refineries, the MPR E-Scan can be used to monitor and control Brix measurement from the beginning of the evaporation stages up to the seed point of crystallization.

The suggested adapter for most installations is either a 316S/S in-line type adapter or a 316S/S vacuum pan adapter. If coating may be an issue, a steam or hot water wash nozzle can be provided.

Sanitary-type adapters designed and manufactured to appropriate 3-A Sanitary Standards are also available if needed.

Industrial Refractometers in Action: Pulp & Paper Mill

This video below highlights various applications for inline refractometers in a pulp and paper mill.

The Electron Machine Corporation pioneered the use of refractometers to accurately measure black liquor dissolved solids nearly 50 years ago. Our long history with this application has resulted in numerous design features that specifically address problems associated with this harsh process measurement. Electron Machine refractometers have been accurately measuring green liquor solids in the paper industry for more than 30 years.

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

Introduction to Industrial Instrumentation

industrial control
Engineer adjusting a
process controller measuring 
the refractive index of a process.
Instrumentation is the science of automated measurement and control. Applications of this science abound in modern research, industry, and everyday living. From automobile engine control systems to home thermostats to aircraft autopilots to the manufacture of pharmaceutical drugs, automation surrounds us. This chapter explains some of the fundamental principles of industrial instrumentation.

The first step, naturally, is measurement. If we can’t measure something, it is really pointless to try to control it. This “something” usually takes one of the following forms in industry:
  • Fluid pressure
  • Fluid flow rate
  • The temperature of an object
  • Fluid volume stored in a vessel
  • Chemical concentration
  • Machine position, motion, or acceleration
  • Physical dimension(s) of an object
  • Count (inventory) of objects
  • Electrical voltage, current, or resistance
  • Refractive Index
Once we measure the quantity we are interested in, we usually transmit a signal representing this quantity to an indicating or computing device where either human or automated action then takes place. If the controlling action is automated, the computer sends a signal to a final controlling device which then influences the quantity being measured.

This final control device usually takes one of the following forms:
  • Control valve (for throttling the flow rate of a fluid)
  • Electric motor
  • Electric heater
Both the measurement device and the final control device connect to some physical system which we call the process. To show this as a general block diagram:

Process control loop
Process control loop
The common home thermostat is an example of a measurement and control system, with the home’s internal air temperature being the “process” under control. In this example, the thermostat usually serves two functions: sensing and control, while the home’s heater adds heat to the home to increase temperature, and/or the home’s air conditioner extracts heat from the home to decrease temperature. The job of this control system is to maintain air temperature at some comfortable level, with the heater or air conditioner taking action to correct temperature if it strays too far from the desired value (called the setpoint).

Industrial measurement and control systems have their own unique terms and standards. Here are some common instrumentation terms and their definitions:

Process: The physical system we are attempting to control or measure. Examples: water filtration system, molten metal casting system, steam boiler, oil refinery unit, power generation unit.

Process Variable, or PV: The specific quantity we are measuring in a process. Examples: pressure, level, temperature, flow, electrical conductivity, pH, position, speed, vibration.

Setpoint, or SP: The value at which we desire the process variable to be maintained at. In other words, the “target” value for the process variable.

Primary Sensing Element, or PSE: A device directly sensing the process variable and translating that sensed quantity into an analog representation (electrical voltage, current, resistance; mechanical force, motion, etc.). Examples: thermocouple, thermistor, bourdon tube, microphone, potentiometer, electrochemical cell, accelerometer.

Refractive Index Transducer
Example of a transducer.
In this case, a
Refractive Index transducer.
Transducer: A device converting one standardized instrumentation signal into another standardized
instrumentation signal, and/or performing some sort of processing on that signal. Often referred to as a converter and sometimes as a “relay.” Examples: I/P converter (converts 4- 20 mA electric signal into 3-15 PSI pneumatic signal), P/I converter (converts 3-15 PSI pneumatic signal into 4-20 mA electric signal), square-root extractor (calculates the square root of the input signal).
Note: in general science parlance, a “transducer” is any device converting one form of energy into another, such as a microphone or a thermocouple. In industrial instrumentation, however, we generally use “primary sensing element” to describe this concept and reserve the word “transducer” to specifically refer to a conversion device for standardized instrumentation signals.

Transmitter: A device translating the signal produced by a primary sensing element (PSE) into a standardized instrumentation signal such as 3-15 PSI air pressure, 4-20 mA DC electric current, Fieldbus digital signal packet, etc., which may then be conveyed to an indicating device, a controlling device, or both.

Refractive Index Transmitter/Controller
Example of a transmitter and/or
controller. In this case, refractive
index signal conditioning electronics
to modify the transducer signal,
and optionally, provide a control
output to a final control element.
Lower- and Upper-range values, abbreviated LRV and URV, respectively: the values of process oC and its URV would be 500 oC.
measurement deemed to be 0% and 100% of a transmitter’s calibrated range. For example, if a temperature transmitter is calibrated to measure a range of temperature starting at 300 degrees Celsius and ending at 500 degrees Celsius, its LRV would be 300

Zero and Span: alternative descriptions to LRV and URV for the 0% and 100% points of an instrument’s calibrated range. “Zero” refers to the beginning-point of an instrument’s range (equivalent to LRV), while “span” refers to the width of its range (URV − LRV). For example, if a temperature transmitter is calibrated to measure a range of temperature starting at 300 degrees Celsius and ending at 500 degrees Celsius, its zero would be 300 oC and its span would be 200 oC.

Controller: A device receiving a process variable (PV) signal from a primary sensing element (PSE) or transmitter, comparing that signal to the desired value (called the setpoint) for that process variable, and calculating an appropriate output signal value to be sent to a final control element (FCE) such as an electric motor or control valve.

Final Control Element, or FCE: A device receiving the signal output by a controller to directly influence the process. Examples: variable-speed electric motor, control valve, electric heater.

Manipulated Variable, or MV: The quantity in a process we adjust or otherwise manipulate in order to influence the process variable (PV). Also used to describe the output signal generated by a controller; i.e. the signal commanding (“manipulating”) the final control element to influence the process.

Reprinted from Lessons In Industrial Instrumentation by Tony R. Kuphaldt under the terms and conditions of the Creative Commons Attribution 4.0 International Public License.

Chemical Recovery in Black Liquor Processing for Pulp and Paper Production

Pulp and paper mill
Pulp and paper mill.
For economic and environmental reasons, pulp mills employ chemical recovery processes to reclaim spent cooking chemicals from the pulping process. At kraft and soda pulp mills, spent cooking liquor (referred to as weak black liquor), from the brown stock washers is routed to the chemical recovery area.

The chemical recovery process involves concentrating weak black liquor, combusting organic compounds, reducing inorganic compounds, and reconstituting the cooking liquor.

Residual weak black liquor from the pulping process is a dilute solution (approximately 12 to 15 percent solids) of wood lignin, organic materials, oxidized inorganic compounds (Na2SO4, Na2CO3), and white liquor (Na2S and NaOH). The weak black liquor is first directed through a series of multiple-effect evaporators to increase the solids content to about 50 percent to form “strong black liquor.”

black liquor
Monitoring percent solids in black liquor
is an important part of chemical recovery.
The strong black liquor from the multiple-effect evaporator system is either oxidized in the black liquor oxidation system, or routed directly to a non-direct contact evaporator (also called a concentrator). Oxidation of the black liquor prior to evaporation in a direct contact evaporator reduces emissions of odorous total reduced sulfur compounds. 

The solids content of the black liquor following the final evaporator/ concentrator typically averages 65 to 68 percent. The soda chemical recovery process is similar to the kraft process, except that the soda process does not require black liquor oxidation systems, since it is a non-sulfur process that does not result in total reduced sulfur emissions.

The concentrated black liquor is then sprayed into the recovery furnace, where organic compounds are combusted, and the Na2SO4 is reduced to Na2S. The black liquor burned in the recovery furnace has a high energy content which is recovered as steam for process requirements, such as cooking wood chips, heating and evaporating black liquor, preheating combustion air, and drying the pulp or paper products. 

The process steam from the recovery furnace is often supplemented with fossil fuel-fired and/or wood-fired power boilers. Particulate matter (primarily Na2SO4) exiting the furnace with the hot flue gases is collected in an electrostatic precipitator and added to the black liquor to be fired in the recovery furnace.
Refractometer for black liquor
Refractometer for black liquor measurement.

The process of chemical recovery must be carefully managed. Process variables such as temperature, pressure, flow and level require robust instruments to ensure safety and accuracy. The measurement of black liquor solids content has relied upon the use of industrial inline refractometers for many decades. The Electron Machine Corporation, with it's ruggedly designed MPR E-Scan,  has established itself as the leader in this process. Incorporating a ruggedly designed sensing head with a 2205 S/S prism holder, sapphire prism, LED light source, and very sturdy electronics, the Electron Machine device delivers on it's claim as the "world's most rugged process refractometer".  Since the refractometer is specifically designed for the very harsh environment of a pulp mill, it promises years of low-maintenance and very reliable operation. 

Happy Fourth of July from Electron Machine

"We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness. — That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed, — That whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness."

THOMAS JEFFERSON, Declaration of Independence

Inline Refractometers for the Production of Jams and Jellies

Refractometers for the Production of Jams and Jellies
Refractometers are used to maintain
standards of jams and jellies.
The quality and uniformity of a food product is paramount to the sales of that product. Assuring that standards are maintained is key to quality and consistency.  Jams, jellies, marmalades, conserves and fruit butters are characterized by concentration of fruit components and sugars. Attention to solids content, pH, and sweetness is essential, and controlling these variables in a production environment requires the proper systems, instruments, and automation.

Jams, jellies, marmalades, conserves and fruit butters are made by boiling fruit and sugar together to give a high solids product, and are characterized by concentration of their fruit components and sugars.

inline refractometer for jam and jelly production
Inline refractometer for jam and jelly production.
Accordingly, standards of identity have been enacted to require specific amounts of the comparatively expensive fruit ingredient. Without these guides, producers could substitute flavored and colored pectin and sugars in place of real fruit.

Definitions:
  • Jam – a product containing both soluble and insoluble fruit constituents.
  • Conserve or preserve – large pieces of fruit are present.
  • Butter - a smooth, semisolid fruit mixture with no fruit pieces or peel. May be spiced
  • Marmalade – are made from citrus fruits and contain some peel.
  • Jelly – is made from filtered fruit juice, no pieces of fruit or insoluble solids present.
In the U.S. jams and jelly products are graded as follows:
  • Fancy  - 50 parts fruit to 50 parts sugar 
  • Standard  - 45 parts fruit to 55 parts sugar 
  • Imitation - 35 parts fruit to 65 parts sugar
  • Fruit butters - At least 5 parts fruit to 2 parts sugar
Standards of identity can be easily formulated with the aid of a refractometer - and instrument that the sugar/solids content by the angle that the solution refracts or bends light. Refractometers are the preferred method of determining of measuring soluble solids and sugars in many food products.

In large scale commercial food production environments, inline process refractometers provide real-time sugar and solids measurement allowing plant operators tight control of product variables so that product uniformity and quality is maintained.

Refractometers for Pulp and Paper Processing

The Electron Machine MPR E-Scan has numerous applications in the paper industry. The most common applications are on black liquor and green liquor. Electron Machine Corporation pioneered the use of refractometers to accurately measure black liquor dissolved solids nearly 50 years ago.


Black Liquor is the waste product from the process of digesting pulpwood into paper pulp by removing various elements to free the cellulose fibers. Electron Machine's long history with this application has resulted in numerous design features that specifically address problems associated with this harsh process measurement.

Green liquor is the dissolved concentration of sodium sulfide, sodium carbonate, and other compounds from the recovery boiler in the paper making process.  Electron Machine Corporation has been actively refining the use of refractometers for measuring green liquor density for over 30 years. The current system uses the 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, minimizing maintenance to allow for a reliable measurement source for on-line automatic control.

The MDS Monitor Divert System is a BLRBAC compliant Black Liquor solids monitoring system designed specifically for Black Liquor recovery boilers. The MDS Monitor Divert System consists of two completely independent MPR E-Scan Hybrid-Digital refractometers with a separate monitor console that supervises the proper operation of each refractometer. The monitor constantly insures that all parameters remain within operational limits and applies the proper divert or alarm actions should a fault or low solids liquor be detected. A built-in printer records all actions with a date and time stamp. The entire system is designed to be user friendly with large daylight-readable color displays and an intuitive menu-driven interface.

The MPR E-Scan also gives paper companies the ability to accurately control the washing line, by detecting changes in the total dissolved solids coming off the washers. This precise measurement allows effective control of the fresh water flow to the washers, reducing excessive water usage. Combining the measurement with data- analysis tools, a company can monitor inefficiencies in the washing line and evaluate the washing results. Allowing improvements in washing efficiency and overall reduction in water. The MPR E- Scan will reduce the overall time needed to meet target dilution. With near instant readings of black liquor concentration and temperature, the instrument removes the reliance on offline testing. 

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

Industrial Refractometers in Brownstock Washing

Pulp and paper mill
Pulp and paper mill.
In pulp and paper production, brown stock washers are used to recover cooking chemicals from pulp production and are critical for maximizing chemical recovery which impacts the financial success and environmental compliance of a pulp mill.

The purpose of brownstock washing is to remove soluble matter from the pulp while using the least amount of water. Efficient washing improves the recovery of cooking chemicals, reduces the use of chemicals during bleaching, increase pulp quality and helps reduce deposit buildup. By utilizing a refractometer to measure the black liquor solids in the feed and outlet stock lines, and the incoming and outgoing filtrate lines, a paper company can experience increased control and cost savings.

The Electron Machine MPR E-Scan gives paper companies the ability to accurately control the washing line, by detecting changes in the total dissolved solids coming off the washers. This precise measurement allows effective control of the fresh water flow to the washers, reducing excessive water usage.

Combining the measurement with data analysis tools, a company can monitor inefficiencies in the washing line and evaluate the washing results. Allowing improvements in washing efficiency and overall reduction in water. The MPR E- Scan will reduce the overall time needed to meet target dilution. With near instant readings of black liquor concentration and temperature, the instrument removes the reliance on offline testing.

The MPR E-Scan is constructed of various alloys to ensure a long service life in a harsh chemical environment. With our customer pipeline adapters, the instruments can be implemented into any process. Due to the unique measurement principle, the instrument's readings are unaffected by bubbles, particles, fibers, color, flow, pressure or vibration. By utilizing the instrument to control and monitor the brownstock washing, paper companies can guarantee that proper dilution was met and maintained.

Electron Machine MPR E-Scan
Electron Machine MPR E-Scan
KEY BENEFITS
  • Increased washing efficiency
  • Continuous accurate control of dilution factor
  • Consistent pulp quality Increased evaporator efficiency
  • Reduced wash loss and decrease wash water
  • Error and Warning light indications Reduced time for correct wash concentration
  • Continuous temperature readings 
Learn more about industrial refractometers and their application in the pulp and paper process by visiting the Electron Machine website at http://electronmachine.com or by calling 352-669-3101.

DCR E-Scan Hybrid-Digital Refractometer

DCR E-Scan
The DCR E-Scan is a hybrid-digital critical angle refractometer. It is used to measure the refractive index of process fluids and may be used as an integral part of a complete process control system.

With an extremely durable Sapphire prism as the foundation, the hybrid-digital design provides digital accuracy with rugged components in the sensing head. This combination produces the essential dependability required for years of use when installed in harsh industrial environments.

The DCR E-Scan is the cost-effective refractometer for an accurate and dependable reading. Electron Machine Corporation calibrates each DCR E-Scan specifically for the intended application. The digital display coupled with the 4-20mA output provides the complete control desired at an affordable cost without sacrificing the rugged reliability desired for today's industrial applications.

Don't Forget Customer Support and Technical Support When Buying Process Instruments

Happy Customer Service
Make sure your vendor's Customer Service and Tech Support
are knowledgeable, experienced, and ENTHUSIASTIC.
Today, many engineers do their product selection largely via the Internet, and usually by just comparing specifications between manufacturers. While this provides a fast, efficient, and objective means to narrow down prospective vendors, it totally ignores a critically important (albeit subjective) component to the success of their project - the vendor's Customer and Technical Support infrastructure.

When choosing a vendor for process instrumentation (industrial refractometers for instance), it's imperative to include an evaluation of the vendor's Technical Support and Customer Support infrastructure. Realizing what these professionals have to contribute, and taking advantage of their knowledge and talent, will save time and money, and greatly contribute to a successful project outcome.

Understanding Why Technical Support and Customer Support are Critical

It's all about two things:
  1. Experience
  2. Attitude

Experience


"If you think it's expensive to hire a professional to do the job, wait until you hire an amateur." Red Adair

By the nature of their job, Customer Service personnel are current on new products, their capabilities and their proper application. Unlike anecdotal information available on the Web, support personnel have first hand knowledge and hands-on experience. They've seen successful (and unsuccessful) product implementation scenarios and are eager to share. A brief discussion about your application with a specialist will guide you toward selecting the best equipment for the requirement. Also, because they are exposed to so many different applications and situations, Customer/Tech Support personnel are a wealth of ancillary application knowledge.

As a project engineer, you may be treading on fresh ground regarding some aspects of fully understanding the project you're working on. You may not have a full grasp on how to handle a particular challenge presented by the application. Calling upon a source with past exposure and experience to your current application prior to product selection will provide a very real, and very valuable benefit.

Attitude:


"Customer service is not a department, it’s everyone’s job." Anonymous

Choose a company that places a huge emphasis on customer service and do some due-diligence. Determine if they're merely providing lip service, or if extreme customer service oozes from the company pores. 

Sam Walton, the founder of Walmart once said "The goal as a company is to have customer service that is not just the best, but legendary." Make sure the vendor you're evaluating sees things the same way.  While reviews or testimonials (if there are any) can be helpful, they should be viewed judiciously. You're going to have to talk to people and get your own "gut-feel".  Do the employee's seem upbeat and happy? Are they knowledgeable? If they can't answer a question, do they volunteer to connect you with someone who can?  Are they enthusiastic?

As an engineer who designs or manufactures a product or process, it's strongly recommended you make the effort to research, contact, and get a first-hand feel for your prospective vendor's Customer and Technical Support Team. Learn about their product and application knowledge, their experience and their commitment to excellence. Taking the time to do this will raise the likelihood that your project will come in on time, on budget and shine brightly upon you.

A BLRBAC Compliant Monitoring System Designed Specifically for Black Liquor Recovery Boilers

MDS Monitor Divert System
MDS Monitor Divert System
The Electron Machine Corporation manufactures a BLRBAC compliant Black Liquor solids monitoring system designed specifically for Black Liquor Recovery Boilers.

The Black Liquor Recovery Boiler Advisory Committee is a group that exists for the purpose of generating safety procedures and guidelines that govern the operation of Black Liquor Recovery Boilers.  The BLRBAC was formed in 1961 by several groups of concerned professionals that had become alarmed by the number of Black Liquor Recovery Boiler explosions. 

The MDS Monitor Divert System consists of two completely independent MPR E-Scan Hybrid-Digital refractometers with a separate monitor console that supervises the proper operation of each refractometer. The monitor constantly insures that all parameters remain within operational limits and applies the proper divert or alarm actions should a fault or low solids liquor be detected. A built-in printer records all actions with a date and time stamp. The entire system is designed to be user friendly with large daylight-readable color displays and an intuitive menu-driven interface.

Isolation Valves are also required to meet the BLRBAC guidelines and allow the refractometer sensing heads to be isolated from an active pipeline should maintenance be needed. The system closely monitors the position of these isolation valves to verify that the refractometers are in service.

All functions of the MDS Monitor Divert System are automatic. For example, should a refractometer fault occur the unit is electronically removed from service and an alarm is activated. Simultaneously the output signal is driven low to warn the operator to disregard this reading. The monitor system then isolates, displays the fault and provides a hard copy record on the built-in printer. Liquor diversion is now controlled by the refractometer in service.
    MDS Monitor Divert System
  • Intelligent purge function- ensures the proper cleaning and extends prism life 
  • Divert trending - provides an actual time left before a diversion when liquor solids are declining 
  • Password protection- to protect critical software areas
The MDS Monitor Divert System is pre-wired and mounted on a panel for easy installation. All customer connections are made to a single terminal strip. Standard output is a 4-20mA for liquor concentration with relay contacts for liquor divert, alarms, and system error indicators. A remote divert input is also available. The system can be provided in an optional stainless steel enclosure with either a vortex-cooler or fan ventilation depending on the specified mounting location.

For more information on the BLRBAC visit here.
For more information on the MDS Monitor Divert System visit here.

Inline Process Refractometers in Tomato Processing

Tomato Processing
Inline Process Refractometers in Tomato Processing
It's obvious that tomato processors have a need to predict product yield, consistency and quality, as these variables directly affect sales and profitability. However, consistency and quality in tomato products is fairly difficult to control because of the fruit variation, harvest maturity, and farming area.

Consumers often select tomato sauces, pastes, purees and dressings based on sweetness levels, so it's very important food producers to accurately control sweetness. The common method for measuring sweetness in this industry is by reading Brix. Degrees Brix (°Bx) is the measure of the amount of sugar in an aqueous solution and is used because it's reliable and fast.

Refractometry is used to determine degrees Brix, and refractometers are the instruments used for the measurement. Very basically, refractometers use a prism to determine how light bends through a substance. The change in light direction is then used to repeatably determine certain values - in this case Brix.

There are several types of refractometers in food processing. Many food processing labs do batch sampling through the use of hand-held refractometers. Another type is the inline process refractometer.  It is used to provide a Brix measuring control loop right on the production line, and can be employed anywhere in the overall process from evaporation stages up to the concentrated final product.

Inline Process Refractometers
Inline Process Refractometer
Inline process refractometers are installed using a sanitary-type pipe adapter, designed and manufactured to appropriate 3-A Sanitary Standards. Should the tomato product be known to produce stubborn coatings on the refractometer prism, a steam port is added to the adapter to allow the prism to be steam cleaned at specific intervals.

The head of the refractometer is mounted directly in the processing line and provides real-time detection of Brix with a measurable output. The refractometer's circuitry then conditions the head's output and compares it to a desired value in a controller. The controller provides a corrective output signal, such as 4-20mA, to a final control element, such as a control valve. The control valve increases or decreases the amount of an ingredient to keep things in balance. Not unlike any other process control variable (pressure, temperature, level or flow), Brix measurement is determined and controlled via it's own control loop by the inline process refractometer,  providing the tomato processor greater control over product quality and consistency.

For more information on the use of inline process refractometers in tomato processing, contact Electron Machine at 352-669-3101 or visit http://electronmachine.com.

Refractometers for Food and Beverage Processing

Refractometers commonly used to detect sugar levels and properties of jams juices, beverages, dairy products and much more.

Electron Machine Corporation developed the first in-line process refractometer more than 50 years ago when orange juice was first concentrated. Since that time, their refractometers have been successfully applied on many more applications including the production of sucrose, fructose, dextrose, soft drinks, fruit juices, dairy, apple sauce, jams, jellies, beer, wine, coffee, tea, vegetable oils, tomato paste, ice cream and honey.

With an extremely durable Sapphire prism as its foundation, the Electron Machine MPR E-Scan combines accurate measurements with ruggedized components in the sensing head combining for years of of dependable and accurate service in harsh food production environments.

Inline Refractometer Adapters, Cleaning Systems & Isolation Valves

There are many different mounting adapters available for the MPR E-Scan refractometer. These adapters have been designed and modified with decades of field experience to provide the most successful installation for specific applications. The video below provides a quick visual tour of the most popular.

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

Understanding the Use of Inline Refractometers in Food and Beverage Production

refractometers for jams and jelly production
Inline refractometers are used
for jam and jelly production to
ensure consistency and quality.
This post is intended to give a basic understanding of the use of inline refractometers in commercial food and beverage production

Refraction

According to Wikipedia, "Refraction is the change in direction of wave propagation due to a change in its transmission medium."

To understand more clearly, consider this. If you place a pencil in a jar of standing in water and look through the jar, it appears to be broken at the water line. When you add sugar to the water, the pencil appears to bend even more. The reason for this is because light travels slower in water than through air. When you dissolve materials (sugar) in the solution, the light will travel even slower.  Understanding this basic concept allows you to understand how you can measure, and therefore control, the concentration on a material in a solution through the use of refraction.

Refractive Index

The refractive index (RI), is the ratio between the speed of light in vacuum and the speed of light in a given media. It determines how much light is bent, or refracted, when entering a material. The Refractive Index of air is 1.0003, and the RI of most gases, liquids, and solids is between 1 and 2.

Refractive Index is defined as:
  • RI= Speed of Light in Vacuum / Speed of Light in a Particular Medium
Applying Refraction to Food and Beverage Processing

Food and beverage industries prefer to use their own units rather than the index of refraction for controlling quality of their product. Examples are measuring sugar content in tomato products, citrus juices, and jams and jellies. These industries prefer to use the % Brix scale, which refers to the sugar concentration. Refractive Index is easily converted to % Brix units through simple calculations.

Inline Refractometers for Large Scale Food and Beverage Production

Industrial inline refractometers directly measure the Refractive Index of process fluids and then display the reading in any number of customer-desired units such as Brix, Percent Solids, Dissolved Solids, etc. 

refractometer in food and beverage process
Inline refractometer in food and beverage process
highlighting sensing element and electronics console.
There are two primary components to an inline refractometer, the electronics console and the sensing head.  

The electronics console usually contains a display of some type, and provides a standard output such as 4-20mA. Optionally, there may be some form of networking protocol such as HART® or RS-232/422. 

The sensing head is installed in line by mounting the prism assembly in a pipe and inserting this pipe section in the process line. Vessel mounting is accommodated by having the prism assembly inserted in a flange that can be attached to a storage tank or mixing tank. 

For more information on any commercial or industrial application for inline refractometers, contact visit Electron Machine at http://www.electronmachine.com or call 352-669-3101.

Industrial Refractive Index Transmitters

Loop diagram
Example flow loop diagram
showing role of transmitter.
Transmitters are process control field devices. They receive input from a connected process sensor, then convert the sensor signal to an output signal using a transmission protocol. The output signal is passed to a monitoring, control, or decision device for use in documenting, regulating, or monitoring a process or operation.

Transmitters are available for almost every measured parameter in process control, and often referred to according to the process condition which they measure.

The refractive index determines how much light is bent, or refracted, when entering a material. When light moves from one medium to another, it changes direction (refracted). This change in the direction of the light can be measured and applied to properties of the material.

Refractive Index transmitter
Example of Industrial Refractive Indextransmitter/controller.
Can act as transmitter alone, or with
optional PID control functions.
Industrial Refractive Index transmitters directly measure the refractive index of process fluids. It then conditions the input signal, making it linear, and then converts that signal into any number of customer-desired units (Brix, Percent Solids, Dissolved Solids, SGU, R.I., etc.) and transmits a standard, linear electrical output (4 to 20 mA) that can be utilized by receiving instruments and displays.

Many transmitters are provided with higher order functions in addition to merely converting an input signal to an output signal. On board displays, keypads, Bluetooth connectivity, and a host of industry standard communication protocols can also be had as an integral part of many process transmitters. Other functions that provide alarm or safety action are more frequently part of the transmitter package, as well.

Industrial Refractive Index transmitters have evolved from simple signal conversion devices to higher functioning, efficient, easy to apply and maintain instruments utilized for providing input to process control systems.

For more information on Industrial Refractive Index transmitters visit Electron Machine at http://www.electronmachine.com or call 352-669-3101.