Increasing competitive, regulatory, supply chain and customer demands have driven the need for process improvement in the pulp and paper industry. In our three-week blog series, Magnetrol® reviews the critical impact that level control makes in improving process efficiencies and safety for pulp and paper mills. This week, turpentine and liquor recovery processes are explored. Next week, we cover plant-wide operations including MC pump standpipes, water storage, chemicals and additives, and lubrication and hydraulic oils. You can also read our first blog article about the pulp and paper industry, which features level measurement applications from chipping to papermaking processes.
Application: Vapors from the digester contain turpentine and 85% of it is released during the relief cycle. Recovery of this volatile organic compound (VOC) is undertaken for environmental reasons, to lessen effluent treatment of condensate, to utilize turpentine as a fuel source, or to sell it as a by-product to chemical processors.
Challenges: Two vessels in a typical recovery system require level control of the turpentine/water interface: the decanter, or separator, and the storage tank. The National Fire Protection Association (NFPA) rates turpentine as a “severe fire hazard.” For this reason, the decanter is contained in a dyked area, storage tanks are sometimes located below ground, and controls must be rated explosion-proof.
– Echotel® Ultrasonic Switch or Thermatel® Thermal Dispersion Switch for point level
– Eclipse® Guided Wave Radar Transmitter or Pulsar® Non-Contact Radar for continuous level
– Atlas® Magnetic Level Indicator for visual indication
Application: Black liquor is the digester waste mixture of spent chemicals and lignin extracted from wood chips. When burned in a recovery boiler, black liquor produces heat for steam and also releases digester chemicals called “smelt.” Mixed with water, smelt becomes green liquor. This is treated with lime in the causticizers to produce white liquor, the digester’s cooking chemical.
Challenges: Stored in varying concentrations, liquors are corrosive solutions with high levels of organic compounds. Liquors can cause chemical burns or damage the lungs if inhaled. Level sensors contend with the chemicals’ harshness, variable density and dielectric, agitation, foaming, and media stickiness. Tank controls should activate the appropriate alarms or emergency shutdown systems.
– THERMATEL Thermal Dispersion Switch for point level
– ECLIPSE Guided Wave Radar Transmitter (with single rod probe) or PULSAR Non-Contact Radar for continuous level