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.

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

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

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

8 Reasons to Partner with Electron Machine Corporation

  1. Our History - We designed & patented the 1st process refractometer in 1957.
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  3. We Solve Problems - Innovative designs that perform far beyond expectations.
  4. Our Experience - 60+ years successfully applying process refractometers.
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What Is An Inline Process Refractometer?

Inline sensing head
Inline sensing head
Inline process refractometers are used in the food processing, beverage, pulp and paper processing, chemical, power, and primary metal industries. Inline process refractometers save labor costs, streamline the manufacturing process, and improve quality by detecting inconsistencies in a product early in the production phase. They continuously monitor, control and report the on Degrees Brix, Percent Solids, Dissolved Solids, SGU, and refractive index of a brand variety of solutions.

Inline process refractometers are made up of three main components:
Control console
Control console
  1. The inline sensing head, which is inserted to a pipe and is exposed the the product for direct measurement. The sensor is connected by a cable to the second main component, the control console.
  2. The control console, which houses the display, electronics, power supply and output connections. Both the sensor and the control module are designed for high accuracy and precise control. Their housing and cabling are often specialized for use in varying extreme conditions and very demanding environments.
  3. The process adapter, which connects the sensor mechanically to the process piping. Adapters are configured for the pipe size and application they are used on and are available in many configurations. Some of the more common adapter options are:
    • Lined - For extremely corrosive applications.
      Mounting adapters
      Mounting adapters
    • Inline - For most applications with pipeline sizes less than 2”.
    • Isolation - For critical process lines that cannot normally be shut down.
    • Sanitary - For applications on a sanitary pipeline.
    • Spool - For most applications with pipeline sizes greater than 2”.
    • Vessel - For applications where the sensing head is to be mounted directly onto a vessel or vacuum pan.
    • Weld-in - For economical mounting.

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

Pulp and paper mill
Pulp and paper mill.
The three major causes of refractometer trouble or failure in black liquor recovery boilers are:
  1. Loss of cooling water and its effect on the sensing head.
  2. Lack of reliability of the prism wash.
  3. Condensation in the sensing head.
These may not apply to all refractometers due to differences in construction and circuitry.

Cooling Water Loss

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

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

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

Prism Wash

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

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

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

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

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

Condensation in Sensing Head

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

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

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

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

Electron Machine Corporation's C.A. Vossberg Receives Distinguished Partner Manufacturing Service Award

2018 FLATE Award Winners
2018 FLATE Award Winners
The Florida Advanced Technological Education Center (FLATE) and the Florida Association for Career and Technical Education (FACTE) awarded Electron Machine's President, C.A. Vossberg, their 2018 Distinguished Partner Manufacturing Service Award.

The Awards represent FLATE’s efforts to
recognize leaders who have been at the forefront of manufacturing workforce education and training.

This is the eleventh year of our FLATE Awards program and is one of FLATE’s many efforts to showcase and recognize the contributions of educators and industries in advancing technician education and training on a regional and statewide level.

Distinguished Partner Manufacturing Service Award
C.A. Vossberg (middle)
Electron Machine, headquartered in Umatilla, Florida, is a premier manufacturer of industrial
refractometers and process control equipment.

For more information, contact Electron Machine by visiting https://electronmachine.com or by calling 352-669-3101.