Showing posts with label BLRBAC. Show all posts
Showing posts with label BLRBAC. Show all posts

BLRBAC Recommended Good Practice Document: Thermal Oxidation of Waste Streams in Black Liquor Recovery Boilers

The black liquor recovery boiler presents problems of operation and safety that far exceed those of the conventional power boiler or other forms of combustion equipment that can be used for the thermal oxidation of waste streams. The recovery boiler is primarily a chemical recovery process unit in which organic materials in the black liquor are burned while the oxidized sulfur compounds of sodium and potassium are reduced and drained as molten smelt from the furnace bottom. At the same time, the heat released is used for generation of steam for power and process.

This document is intended to address concerns of the industry relating to safe thermal oxidation of waste streams in recovery boilers. “Waste streams” for this document are produced in the pulping process. The major waste stream is noncondensible gases (NCG), which are gases that contain reduced sulfur compounds from the digester and evaporator operations and are a source of odor.

The following list is representative of the pulping process waste streams that are addressed:
  • Dilute Noncondensible Gas (DNCG)
  • Concentrated Noncondensible Gas (CNCG)
  • Stripper Off Gas (SOG)
  • Chip Bin Noncondensible Gas (CBNCG)
  • Dissolving Tank Vent Gas (DTVG)
  • Soap
  • Methanol
  • Turpentine
  • Tall Oil
  • Spent Acid
  • Secondary Sludge

MDS Black Liquor Solids Monitoring System Training by Electron Machine Corporation

Electron Machine Corporation offers free MDS training at our facility in Umatilla, Florida. The MDS Monitor Divert System is a BLRBAC compliant Black Liquor solids monitoring system designed specifically for Black Liquor recovery boilers. Classes cover theory, operation, maintenance, troubleshooting and correct usage of the isolation valve. Training is comprehensive, friendly, personalized and provides the hands-on know-how necessary to operate the MDS.

For more information contact Electron Machine Corporation at 352-669-3101 or visit

Electron Machine Attends 2018 Fall BLRBAC Meeting

Electron Machine
C.A. Vossberg and Jack Wilburn of Electron Machine exhibiting at
BLRBAC 2018 Fall Meeting

The BLRBAC Fall Meeting was held in in Atlanta this past October and Electron Machine was pleased to attend and exhibit.

The BLRBAC is a  trade association that exists for the purpose of sharing knowledge, drafting guidelines, and maintaining those guidelines to help facilitate the safe and reliable operation of Black Liquor Recovery Boilers.

The sodium sulfate or kraft pulping process is used to produce pulp for the production of paper.  Black Liquor Recovery Boilers reclaim the spent combustible pulping chemicals in black liquor and create steam. If not for the advent of the black liquor recovery boiler (BLRB), this pulping process would not be economically viable.

BLRBAC’s objective is to promote improved safety of chemical recovery boilers and their auxiliaries through the interchange of technical knowledge, experience, and data on past and any future recovery boiler incidents.

Electron Machine has been an active member of the BLRBAC for over five decades and supports the very valuable work the BLRBAC does to improve safety, operation and efficiency of chemical recovery boilers.

Inline Process Refractometer Application Engineering Data: Heavy Black Liquor

Heavy Black Liquor RI vs. Concentration

Refractometers are used in the recovery boiler area to measure heavy black liquor solids in the range of 50-80%. When used to monitor liquor solids to the spray nozzles they become so critical that the recovery boiler will not be operated without them.

As quoted from the Black Liquor Recovery Boiler Advisory Committee, “Refractometers have proven to be effective for black liquor recovery boiler service.” Refractometers are a critical component of the black liquor safe firing system.

Monitoring the recovery boiler firing liquor concentration requires two refractometers in a redundant and specially supervised system. A “Monitor Divert System” employs supervisory circuitry to oversee the correct operation of the refractometer and perform certain logic functions if it detects a failure. The most important of these is the automatic
diversion of the liquor from the furnace into a recirculation loop until the problems can be resolved.

Refractometers used elsewhere in this area include measuring the concentration of the heavy black liquor from storage as it enters the recovery area. They are also used extensively around the cascade or cyclone evaporators to monitor the performance of the direct contact evaporation system. When refractometers are used in the recovery area, the process can be tuned to operate efficiently and most importantly, more safely.

Inline process refractometer on black liquor service
Inline process refractometer on black liquor service.

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

A presentation to the Western Canada Black Liquor Recovery Boiler Advisory Committee (BLRBAC) by Electron Machine Corporation. The presentation slides were made in to this video for viewing on YouTube.

What is the BLRBAC?

The BLRBAC stands for Black Liquor Recovery Boiler Advisory Committee. It was formed in 1961 as a non-profit trade association dedicated to improved safety of chemical recovery boilers, and their auxiliaries, through the interchange of technical knowledge, experience, and data on past and any future recovery boiler incidents.

It's formation stemmed from an alarming number of explosions, injuries, and deaths involving Black Liquor Recovery Boilers. Industry professionals from insurance companies, paper companies, and boiler companies agreed to create the BLRBAC for the purpose of generating safety procedures and guidelines that govern the operation of Black Liquor Recovery Boilers.

The BLRBAC has a number of active sub-committees that are constantly reviewing and updating their safety guidelines to reflect current technology and knowledge.

The Black Liquor Recovery Boiler Advisory Committee meets twice a year in Atlanta GA, usually the first week in April and October.

For more information about the BLRBAC, visit

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

recovery boiler
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.

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 or call 352-669-3101.

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.