Pneumatic Actuators that Stand Up to Pulp and Paper Plants

Simplified Pulp and Paper Process Diagram

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. One reason why the kraft process dominates the paper industry is because of the ability of the kraft chemical recovery process to recover approximately 95 percent of the pulping chemicals and at the same time produce energy in the form of steam.

The purpose of the chemical recovery cycle is to recover cooking liquor chemicals from spent cooking liquor. The process involves concentrating black liquor, combusting organic compounds, reducing inorganic compounds, and reconstituting cooking liquor.

Chemical recovery process flow diagram.

Green liquor is created when molten inorganic salts, referred to as "smelt," collect in a char bed at the bottom of the furnace. Smelt is drawn off and  dissolved in weak wash water to form a solution of carbonate salts - known as green liquor - which is primarily Na2S and Na2CO3. Green liquor also contains insoluble unburned carbon and inorganic Impurities, called dregs, which are removed in a series of clarification tanks.

Decanted green liquor is transferred to the causticizing area, where the Na2CO3 is converted to NaOH by the addition of lime (calcium oxide [Ca0]). The green liquor is first transferred to a slaker tank, where Ca0 from the lime kiln reacts with water to form calcium hydroxide (Ca(OH)2). From the slake, liquor flows through a series of agitated tanks, referred to as causticizers, that allow the causticizing reaction to go to completion (i.e., Ca(OH)2 reacts with Na2CO3 to form NaOH and CaCO3).

On the right you see a Kinetrol model 14 double acting actuator on a 8” full-port ball valve on a green liquor line. The valve cycles 2 times per day to direct green liquor flow and weak wash (weak white liquor) alternatively from one pipe to another in order to prevent solids build up in the pipelines.

Equipment used to produce pulp, paper, and paperboard is exposed to a wide range of temperature and humidity conditions, and contaminants. Actuators used in Pulp and Paper manufacturing processes must withstand the most difficult operating conditions.  Kinetrol actuators are preferred in these situations because they don't allow corrosive atmospheres to penetrate the actuator or springs, their long cycle life,  and their epoxy stove enamel finish.

Contact the experts at Kinetrol USA at 972-447-9443 to discuss any pulp and paper mill actuator application.

Choosing the Right Valve Actuator for Pulp & Paper Processing

In pulp and paper mills there are many hazardous, corrosive and reactive chemicals used in the chemical pulping process.  This particularly hostile atmosphere demands properly engineered automated valve systems and ruggedized valve actuators, spring units, and positioners.

If you understand the basics of how paper is made, and what chemicals are normally found in the environment, you'll understand immediately why special attention needs to be taken for valve and actuator selection. 

In the early stage of paper production, during the separation of pulp from wood chips, digesters combine high heat and a strong alkaline liquid called "white liquor" to turn wood chips into pulp. The white liquor breaks down the lignin (the material that holds the wood fiber together) in wood chips and mixes with the white liquor to form a by-product referred to as "black liquor".  Another by-product of this process is Hydrogen Sulfide, a poisonous, corrosive, and flammable gas. 

8" valve on a green liquor line
with Kinetrol Model 14

Black liquor is then sent to recovery boilers where molten solids - namely Sodium Sulfide, Sodium Carbonate - are formed. These molten solids are sent to tanks and mixed with water to become "green liquor". 

While this phase of the process presents challenges to valve and actuator selection, the use of and exposure to harsh chemicals and compounds is not limited to the wood chip/pulp separation stage. 

Later in the paper production process, the pulp is washed, screened and bleached. During this phase, valve actuators are exposed to atmospheres containing many other aggressive compounds such as Oxygen Chlorine, Hydrogen Peroxide, and Ozone.

Proper selection of valves and actuators is critical for worker safety, plant safety, and for the quality of the paper production. All components - valves, actuators, spring units, and positioners - need to be carefully selected to provide safe operation, redundancy, optimum control, and optimal service life.

Kinetrol products are designed for just such service and have an outstanding reputation in these applications. To find out how and why, visit http://www.kinetrolusa.com or call 972-447-9443.

Tough Actuator Service on Paper Plant Green Liquor Line

Pulp and Paper Plant

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 process equipment, piping, and valves to very tough environments. Kinetrol actuators are preferred in these situations because they don't allow corrosive atmospheres to penetrate the actuator or springs, their long cycle life,  and their epoxy stove enamel finish.

Below is a picture of a Kinetrol model 14 double acting actuator on a 8” full-port ball valve on a green liquor line. The valve cycles 2 times per day to direct green liquor flow and weak wash (weak white liquor) alternatively from one pipe to another in order to prevent solids build up in the pipelines.

Kinetrol Model 14 in Green Liquor Line