Inline Process Refractometer Application Engineering Data: Heavy Black Liquor

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.

What Is An Inline Process Refractometer?

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

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

• 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.

Technical Sales Representatives: The Often Underutilized Asset

Work with your technical sales rep.
It will pay off in ways you haven't imagined.

Process refractometers are sold with the support of sales engineers working for the local distributor or representative. By realizing what these specialists have to contribute, and taking advantage of their knowledge and talent, you will save time and money and experience a better project outcome.

Consider these contributions:

Product Knowledge:
Sales engineers, by the nature of their job, are current on new products, their capabilities and their proper application. Unlike information available on the Web, sales engineers get advanced notice of product obsolescence and replacement. Also, because they are exposed to so many different types of applications and situations, sales engineers are a wealth of tacit knowledge that they readily share with their customers.

Experience:
As a project engineer or leader, you may be treading on fresh ground with a refractometry requirement for your current assignment. You may not have a full grasp on how to handle a particular challenge presented by a project. If this is the case, call in the local technical sales representative - there can be real benefit in connecting to a source with past exposure to your current requirement.

Of course, sales engineers will be biased. Any solutions proposed are likely to be based upon the products sold by the representative. But the best sales people will share the virtues of their products openly and honestly, and even admit when they don’t have the right product. This is where the discussion, consideration and evaluation of several solutions become part of achieving the best project outcome.

Whatever your stake in an upcoming or ongoing project, it's highly recommended you develop a professional, mutually beneficial relationship with a technical sales expert, a problem solver. Look at a relationship with the local sales engineer as symbiotic. Their success, and your success, go hand-in-hand.

PID Control: The Basics

PID diagram (courtesy of Wikipedia)

PID is short for "proportional plus integral and derivative control", the three actions used in managing a control loop. Process loop controllers use one, two or all three of these to optimally control the process system. PID control is used in a wide variety of applications in industrial control and process system management.

Many types of PID controllers exist on the market and are used for controlling temperature, pressure, level and flow. PID control is also used in industrial, inline refractometers to control process variables such as Brix, Percent Solids, Dissolved Solids, Specific Gravity Units, and Refractive Index. 

Here is a brief explanation of the three actions that make up PID control.

Proportional Control Action (P): The controller output responds in proportion to error signal. The characteristic equation for this action is:

• Where, Kp is called proportional gain, e is the error magnitude and B is the output from controller when there is no error. It is also called bias. 
• In a proportional controller, the value of gain is set as required by the process and can be varied from 0 to ∞. 

Integral Control Action (I): The control system will respond if the error is present over a period of time. This type of control action is called Integral Control Action. The integral action is defined mathematically as:

• Where, e= error, Ti= Time interval of integral action.
• Purpose of integral action is to provide adequate control action on varying demands of process. In this type of action, output varies as per the time integral of error. This action does not exist independently and always associated with proportional control. 

Derivative Control Action (D): To achieve a stable process, wide proportional band and low integral action are set. Due to these settings, the control system can be too slow. If large system disturbances occur over a wide interval, PI controllers are inadequate. These large system disturbances can be managed if the controller output responds not only to the magnitude of deviation, but also to the rate of change of deviation. Derivative control action is that control action. 

Today's process controllers are much easier to set the PID, thanks to auto-tuning algorithms. What used to be a very time consuming and tedious job can now be done with the push of a button and allowing the controller to "learn" the process dynamics. PID controllers minimize error and optimize the accuracy of any process.

For more information on the use of closed loop control with industrial inline process refractometers. contact Electron Machine Corporation by visiting http://www.electronmachine.com or calling 352-669-3101.