Chemical Recovery in Black Liquor Processing for Pulp and Paper Production

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.”

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 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. 

For more information about inline process refractometers for black liquor processes visit this link or contact Electron Machine at 352-669-3101. 

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 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.

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.

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

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

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.

DCR E-Scan Digital Hybrid Refractometer from Electron Machine Corporation

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

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.