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On-line Freeness Analyzer - Drainac IIIB

Drainac ™ Drainage Rate Indication System. An on-line instrument that continually measures the drainage rate of stock being sampled from any stock line with a minimum working pressure of 20 psig. The output is a proportional 4-20mA DC signal. The unit consists of two major sub-assemblies; a detector and a detector control cabinet.

Detector -

The detector assembly consists of a 2" diameter, 316SS, vertical riser partitioned from the transparent acrylic tube by a 316SS perforated screen. The riser includes a 316SS full port ball valve for isolation and a stock line pressure transmitter. Within the transparent tube are 316SS conductance probes for filtrate level detection and a spray nozzle for cleaning the screen. Furnished with the detector are solenoid valves for control of flush water to the spay nozzle, tube / electrode wash, and under screen tangential swirl. The detector is hinged to provide screen access (24" minimum height required). Services required are flush water and air pressure at a minimum of 10 psig above the maximum stock line pressure.

Detector Control Panel -

A stainless steel wall-mounted 20" x 20" x 6" NEMA 4X cabinet (floor-mounted pedestal optional) is provided for electronic and pneumatic support circuits, stock line pressure gauge, and detector tube pressure gauge. An industrial microprocessor provides level sensing, sequencing logic, blow down and flush time control, freeness calculation, automatic calibration, and graphic display of the information to the operator. An isolated output of 4-20 mA DC will drive up to 900 ohms of maximum load. Air filter / regulator with pressure gauge included. The cabinet will have external on / off switch and internal components tubed and wired, with user connections labeled.

Principle of Operation

Pressure in the detector chamber above the screen is alternatively biased negative and positive with respect to the stock line pressure. During negative pressure, stock rises to the screen. The stock builds a fiber mat on the screen which the filtrate must pass to rise into the measurement chamber. The rate of rise of the filtrate in the chamber is the drainage rate. The time required to fill the detector from the lower to upper level probe is measured and the corresponding freeness is calculated. The result of the calculation is converted and outputted as a proportional 4-20 mA DC signal. The detector pressure is then made positive with respect to the stock line pressure, forcing the fiber mat downward back into the stock line. Flush water is then admitted through the three entries during the exhaust phase to ensure the detector is clean. The cycle is then repeated.

The Drainac ™ IIIB includes a very effective, simple engineering design to compensate for significant changes in process variables that can affect freeness, specifically, pressure, consistency, temperature, and pH. Normal changes in these variables for any given grade will have no meaningful effect on the instrument's ability to measure freeness. However, grade changes requiring a major shift in one or more of these four variables can easily and accurately be handled by Drainac ™ IIIB through the use of the multiple calibration characteristics. The microprocessor has the capability to retain up to (10) ten different setting and calibration parameters.

Product Information

• Overhead clearance of 24" above the stock line surface is required. The detector tube must be mounted in a vertical position. The detector will hinge back to allow for operator access for cleaning.
• The detector subassembly may be installed in a vertical position anywhere it is desirable to measure the drainage rate of the stock. The stock line pressure should be between 20 psig and 90 psig.
• The Drainac ™ IIIB can be applied in consistencies ranging from 0.5% to 6.0%. The range in which consistency will have no noticeable effect on the Drainac ™ IIIB reading is ± 5% of nominal. (i.e. 2.85% to 3.15% for nominal 3%).
• The stock line should be flowing full with velocity between 1-10 fps. The stock flow should be free of entrapped air.
• Air pressure of 10 psig greater than maximum stock line pressure must be available (minimum 30 psig).
• Fresh water must be available for detector flush at a pressure of 10 psig greater than the maximum stock line pressure.
• Standard electrical requirements are: 120 volts, 50 or 60 Hz, single phase.
• The length of the vertical riser on the detector will be sized in accordance with the size of the stock line. Please refer to the Application Data Sheet upon order placement.
• The effect of stock temperature change is negligible. An increase in temperature decreases the viscosity of water, but increases the compactability of the fiber mat, increasing its drainage resistance. These two effects tend to be self-canceling. A temperature change of ± 10°F will, in general, result in no noticeable change in the reading.