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.

The World's Most Rugged Process Refractometer

Built for the most demanding industrial applications, Electron Machine process refractometers are designed from the ground up to handle abuse. From hot, dirty, and harsh environments in chemical plants and pulp mills, to the caustic wash downs and constant vibration in food and beverage processing, EMC process refractometers stand up to the punishment.

Electron Machine's reputation for building the world's most rugged process refractometer isn't an accident. They been providing durable, safe, reliable, and accurate process measurement and control instrumentation for more than 70 years. 

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Process Refractometers Maintain Product Quality in Commercial Food and Beverage Production

Process Refractometer (sensor)
(Electron Machine Corp.)

All commercial food products are selected on the basis of quality, freshness and affordability. Varying product quality is the best way to lose brand-loyal customers. Quality and consistency can be different between brands, but they cannot vary within a brand.

Manufacturers of juices, jellies, honey, wine, and carbonated beverages rely on the measurement of "Brix" to control product quality and consistency. Brix (symbol °Bx) is defined as 1 gram of sucrose in 100 grams of solution, and represents the strength of the solution as percentage by mass.

Examples of food and beverage products that need to carefully measure sucrose, fructose, and dextrose include soft drinks, fruit juices, dairy, apple sauces, jams, jellies, beer, wine, coffee, tea, vegetable oils, tomato products, and honey.  To do this, a device known as a refractometer is used to measure Brix (as well as other dissolved solids).

In smaller food and beverage applications, the refractometer is a handheld device used for batch sampling, but for high volume commercial processing, a more robust and heavy duty "process refractometers" is used. Sometimes referred to as "inline refractometers", these process instruments provide real-time, continuous measurement of Brix and dissolved solids.

Process Refractometer with
sensor mounted on sanitary
pipe shown with control box.
(Electron Machine Corp.)

This category of process refractometer is designed to provide very accurate and repeatable measurement for products flowing through a pipe or mixing in a vessel. They are designed to handle higher temperatures, resist contamination and corrosion, and they respond very quickly to any process deviation.

A process refractometer works by shining an LED light source from a range of angles, through a product sample, onto a prism surface. By measuring the difference in the reflection and refraction of the light source, a critical angle can be determined and the refractive index can be accurately calculated.  This measurement and calculation can be done accurately, repeatably, and quickly, making process refractometers the de-facto standard for the measurement of Brix in high production  food processing applications.

For more information on the use of process refractometers in food and beverage production, visit this link.