Inline Refractometers Tough Enough for Paper Plant Black and Green Liquor Lines

Refractometer and HPC Adapter with High Pressure Purge System
Refractometer and HPC Adapter
with High Pressure Purge System

It's said the only thing a pulp and paper plant doesn't reuse is the "shade the building casts". The processes used in the production of pulp and paper are very efficient when you consider the reuse of energy and by-products. The efficiency comes at a cost though - through very hostile atmospheres and demanding operating conditions for process equipment.

For example, the "kraft process" (also known as the sulfate process) is the method to convert wood chips into pulp and then to cellulose fibers. This is done by mixing the wood chips with sodium hydroxide and sodium sulphate, soaking, cooking and processing.

Here's a very basic explanation of the kraft process. Wood chips are soaked and processed in sodium hydroxide and sodium sulphate mixture known as "white liquor". After the wood chips are impregnated with white liquor, they are then cooked in digesters to break the wood down into cellulose. The solid pulp is then separated and the remaining fluid is referred to as "black liquor". Black liquor is further processed to remove solids and chemicals which are to be re-used in the pulping process. One of the final by-products is "green liquor" which contains sodium carbonate and sodium sulfide and is then reacted with lime to regenerate more white liquor.

All of these steps expose instruments, process equipment, piping, and valves to very tough environments. Electron Machine Corporation, a manufacturer of extremely rugged inline process refractometers, has been actively refining the use of refractometers for measuring green and black liquor density for over 30 years.

The scaling associated with these applications results in an optical coating on the refractometer sensing head. If this scaling can be controlled to allow an acceptable duration of on-line measurement, and then effectively removed when coating occurs, the accuracy of the refractometer can be fully utilized with minimal maintenance. The primary issue then becomes the maintenance required to keep the cleaning system operating effectively.

Electron Machine's efforts led to a system using their "almost indestructible" MPR E-Scan Refractometer combined with heated high-pressure water for cleaning. The resulting combination provides an effective removal of optical coatings by reducing thermal changes and minimizing maintenance to allow for a reliable measurement source for on-line automatic control.

If you're interested in refractometry in pulp and paper processing, look no further than Electron Machine. They have the history, the experience, and the toughest inline refractometer on the planet.

For more information, visit or call (352) 669-3101.