White water is a fine particle slurry used throughout the paper making process. Its name derives from fine fiber particles in the water that give it a milky white appearance. White water drains from the paper stock into a pit below the paper machine and is used for a variety of uses in the paper making process.
White water systems must periodically be cleaned to remove bacterial build up that occurs over time. This process is known as boil-out, in which the white water is raised to near boiling temperatures of around 180°F – 190°F (82°C – 88°C) to kill any bacteria in the system. A caustic solution is sometimes added to shorten the process and increase the effectiveness. The water is held at temperature until all bacteria is killed.
White water systems are typically heated by heating tank contents with steam spargers in the white water chest. Steam Injection Heaters that use a steam pressure reducing valve (PRV) experience a pressure drop in the steam pressure which leads to low velocity steam flow. Low steam velocity leads to poor steam mixing. Externally controlled steam injection heaters may lead to:
- Ineffective condensation of the steam from the spargers, damaging the chest walls leading to expensive repairs
- Steam escaping from the tanks and venting to atmosphere
- Hot and cold zones to be present in the whitewater chest, leading to variable stock temperatures at the paper machine head box
PSX Heater Solution
A PSX Jet diffuser heater is installed in the white water system to quickly raise the white water temperature to near boiling and then throttle back to maintain the desired temperature.
ProSonix unique method of steam injection utilises an internal steam control to precisely deliver the appropriate mass flow of steam for the required heating. This is achieved via and integral Pneumatic Actuator, and a variable position stem plug in the steam jet diffuser. We do not throttle or regulate steam pressure. This design offers a precise method of steam control through a choked flow control delivery of the steam. Choked flow is the phenomenon of accelerating a vapor to maximum velocity by creating a pressure differential through an engineered nozzle. By establishing choked flow, the steam mass flow can be metered to precisely control the heating of the liquid.
Key Direct Steam Injection Benefits
- Energy savings resulting from faster tank time and reduced heat loss to atmosphere
- Lower maintenance due to the PSX heater’s self cleaning design
- Improved safety due to better steam injection heating methods (elimination of steam hammer)
- Reduced operating costs by reducing costly machine down time
- Faster tank heat up time (~ 6-8 times that of traditional sparging) equals less machine downtime
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Wet end starch – Starch added at the wet end to the paper slurry can help increase the sheet strength. The starch will also act as binder for various additives and fillers such as Alum, Calcium carbonate and TiO2. When properly cooked, starch swells and its viscosity increases. Wet end starch is produced to give it a cationic charge. This allows the cooked starch natural adhesion properties to create a bond with the paper fibers. By connecting the fibers and additives in small ‘clumps’, leaving relatively clean water in between (flocculation), faster drainage of water leading to increased wire and machine speeds.
Kraft pulp mills produce pulp from wood chips. Within the pulp production, a chemical process produces green liquor. Green liquor is a combination of recovery boiler smelt and dilute white liquor. Dregs are removed and liquor is sent to recausticising tanks to produce white liquor. Flows vary based on the size of the pulp mill and can range from 350-1400 gpm.