Fisher Pulp and Paper Solutions ® Reliable control valve technologies for on-specification product.
| Fisher® Pulp and Paper Solutions Discover the Right Solution for You The pulp and paper industry, in recent years, has seen some difficult times. However, it’s likely that no other manufactured product plays a more significant role in daily human activity than paper products. Paper provides the means to recording and disseminating most of today’s information, news, and data.
Fisher® Pulp and Paper Solutions | 3 Papermaking Overview The Process of Papermaking Although not present at all mills, there are six major steps to the papermaking process: mechanical preparation of the wood into wood chips, turning wood chips into pulp (digestion), chemical recovery, pulp whitening through bleaching, pulp stock preparation, and finally paper formation. The first of these steps uses strictly mechanical processes to form small chips from the logs supplied to the mill.
| Fisher® Pulp and Paper Solutions Damaging Effects of the Papermaking Process Material Damage Excessive Noise and Vibration Physical damage to control valves can mean high maintenance costs, lack of predictability of the damage, and unplanned shutdown or downtime. Damage can consist of a mechanical and/or selective chemical nature on material surfaces. Noise control is crucial to achieving compliance with environmental and workplace regulations.
Fisher® Pulp and Paper Solutions | 5 Cavitation Flashing Simply stated, cavitation is the formation and collapse of cavities in a flowing liquid. It becomes critically important for appropriate valve sizing, selection of products and materials, and cavitation mitigation technologies to ensure problems do not arise. Emerson provides a wide range of cavitation control technologies for clean or dirty service.
| Fisher® Pulp and Paper Solutions Optimize Your Process, Maximize Your Profitability Control Valve Selection and Design Reliable Fluid Control Selecting a control valve is more of an art than a science. Clearly, a single product design is not sufficient for the wide variation of applications across the entire pulp and paper process. Emerson uses multiple approaches to address application-specific issues.
Fisher® Pulp and Paper Solutions | 7 Serving You Through The Life of Your Plant Click on the QR code to find the sales office nearest you. Parts Service Confidence in papermaking solutions relies on true OEM engineering and manufacturing specifications. Replicator parts typically do not last as long as genuine Fisher parts, so you have to replace them more often.
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| Fisher® Pulp and Paper Solutions Cooking Caustic Addition Product Solutions Chips are fed via a screwfeeder into the top of a digester where it is mixed with cooking liquor then cooked to a schedule. The cooking liquor, sodium hydroxide (NaOH) solution, is a caustic chemical used with sodium sulfide to create white liquor. This fluid is used to break down the lignin that binds cellulosic fibers while in the digester.
Fisher® Pulp and Paper Solutions | 11 Cooking Digester Liquor Level Control Continuous digester liquor level control is a critical and demanding application. The liquor level is critical to digester operational stability, providing correct throughput, and reducing kappa variation (lignin measure in the pulp). Found in the make-up liquor line after the make-up liquor pump, the control valve controls liquor flow to the top of the impregnation vessel in a two vessel system.
| Fisher® Pulp and Paper Solutions Cooking Digester Switching In a continuous digester’s cooking zone, cooking liquors are circulated in loops to add the appropriate heat and chemicals to cook the wood chips. Valves control the circulating liquor as it travels from the screens lining the interior of the digester, to the circulation pump, through the heat exchanger, and returns the liquor to the digester cooking zone.
Fisher® Pulp and Paper Solutions | 13 Cooking Digester Blow After the wood chips are sufficiently cooked, they must be discharged from the digester. Digester blow valves, typically found at the bottom of digesters and/or near the top of the blow tank, ensure pulp stock retains its integrity while still allowing all cooking liquors to be recovered. However, insufficient discharge can ruin valuable pulp and cause loss of expensive steam and cooking liquors.
| Fisher® Pulp and Paper Solutions Cooking Batch Digester Gas Relief A batch digester is essentially a large pressure cooker. As steam is applied to the mass of chips and liquor, a quantity of resinous vapors are distilled off. These vapors, along with entrained air in the chips and a small quantity of non-condensed steam, can collect at the top of the digester.
Fisher® Pulp and Paper Solutions | 15 Pulping Brown Stock Rejects Pulp from cooking always contains some unwanted solid material. Some of the fibrous material may not be completely in the form of individual fibers. The main purpose of the pulp screening process is to separate harmful impurities from pulp with minimal fiber loss, and at an acceptable cost level. Bark, sand, shives, and rocks are typically found within the cooked chips and must be removed.
| Fisher® Pulp and Paper Solutions Pulping Medium Consistency Pump Discharge Medium consistency pumping (dry solid content between 8-18%) and chemical mixing systems are the most important stock transfer equipment in the modern oxygen delignification and bleaching processes, with recycled fiber and in mechanical pulp lines. These valves can be used in two distinct ways: with variable speed pumps, the valve is run at full 90 degrees open, and with static head pumps, the valve needs to be throttled.
Fisher® Pulp and Paper Solutions | 17 Bleaching Chlorine Dioxide Addition After digestion, end products that are required to be whitened go to the bleach plant. Chlorine dioxide has rapidly become the industry standard bleaching agent because of its selectivity in destroying pulp lignin without degrading cellulosic fibers, thus preserving pulp strength and providing stable brightness.
| Fisher® Pulp and Paper Solutions Recovery Black Liquor Evaporation The change of weak black liquor to strong black liquor via an evaporation plant allows black liquor to be burned as fuel in the recovery boiler and serves as the major application in the recovery cycle of the paper mill. The main purpose of the evaporation plant is to increase the dry solids content of the black liquor by evaporating water until reaching a concentration suitable to allow burning in the recovery boiler.
Fisher® Pulp and Paper Solutions | 19 Recovery White Liquor Pressure Filter Switching The white liquor pressure filter is the preferred method for separating white liquor slurry into its primary components of white liquor and lime mud. This slurry is pumped through the feed valve into the filter vessel where the fluid is forced through a filter. The solid lime mud cannot pass through the filter and cakes onto the filter itself.
| Fisher® Pulp and Paper Solutions Recovery Black Liquor Guns Black liquor from the evaporator set is introduced into the recovery boiler via liquor guns. These guns produce a spray that is combustible by a hot flue gas. The spray is controlled by a valve that is subjected to corrosion due to high black liquor content. Additionally, this valve must precisely control the black liquor flow as this can directly affect the recovery boiler’s burning and steam generation efficiency.
Fisher® Pulp and Paper Solutions | 21 Paper Machine Paper Additives Prior to stock entering the headbox, various additives are combined with the pulp during stock preparation. For instance, the combination of rosin size and aluminum sulfate resists penetration by fluids, and is critical for ink printing operation. Other agents and starches help increase the paper’s internal strength.
| Fisher® Pulp and Paper Solutions Paper Machine Basis Weight Pulp stock consistency is a key factor in determining the grade and quality of the end product. Basis weight measured at the dry end of the machine is fed back via control logic to the basis weight valve at the wet end of the machine. Appropriate adjustments can then be made to produce an end product that meet’s customer specifications. This makes the basis weight valve one of the most critical in the mill.
Fisher® Pulp and Paper Solutions | 23 Paper Machine Vacuum Box After the pulp stock is sprayed on the forming fabric, the sheet is still very wet and must be removed. A vacuum box, or flatbox, under the forming fabric helps to remove the excess water. These valves help to control the amount of vacuum being pulled on the sheet, and can have a big effect on the rest of the paper machine.
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| Fisher® Pulp and Paper Solutions Power and Steam Cycle Boiler Feedwater Startup and Regulating In the normal range of plant operation, the boiler feedwater regulator experiences high flow rates with low differential pressure. However, during startup, this valve experiences low flow rates with very high differential pressure, which can cause severe cavitation damage. Some feedwater systems are designed using one valve to handle startup and normal operating conditions.
Fisher® Pulp and Paper Solutions | 27 Power and Steam Cycle Sootblower In the power and recovery boiler, firing fuels such as coal, oil, or other waste products cause degradation of the boiler tubes. Deposits from the combustion process can collect on the heat exchanging tubes, which reduces thermal efficiency and may cause operational problems.
| Fisher® Pulp and Paper Solutions Power and Steam Cycle Sky Vent Sky vent valves may operate during startup and shutdown of the heat recovery steam generator, bypassing main steam around the steam turbine to the atmosphere. Sky vent valves must withstand the full pressure drop that occurs as the valve dumps high pressure and temperature steam directly to the atmosphere. They should operate quietly during dump operation and provide tight shutoff during normal operation to prevent valuable steam leakage.
Fisher® Pulp and Paper Solutions | 29 Power and Steam Cycle Main Steam Pressure Reduction Most mills need to accommodate a variety of steam pressure requirements for the various processes in the mill. Steam from the power and recovery boilers supply high pressure and temperature steam to the high pressure header, and can be staged down to accommodate the pressures needed at the other headers.
| Fisher® Pulp and Paper Solutions Power and Steam Cycle Turbine Bypass Turbine bypass systems permit operation of the steam generator independently of the turbine during startup, shutdown, and plant upset conditions. They must be adequately sized to meet the needs of normal startup and shutdown, as well as transients. They must also operate at acceptable noise levels.
Fisher® Pulp and Paper Solutions | 31 Power and Steam Cycle Steam Conditioning As with any superheated steam cycle, the temperature of the superheat needs to be controlled to ensure that it does not exceed the material limits of the process equipment. Temperature control is accomplished by use of an attemperator or desuperheater that injects a controlled amount of cooling water into the superheated steam flow.
If you found this brochure valuable, may we also recommend the following literature: “Fisher® Pulp & Paper Sourcebook” “Fisher® Power Industry Solutions” Fisher Power Solutions ® Document Number: D103540X012 www.EmersonProcess.com/Fisher/ Documentation Control valves engineered to improve your plant performance. Document Number: D351920X012 www.EmersonProcess.com/Fisher/Documentation “Fisher® Vee-Ball Rotary Control Valves” Document Number: D350004X012 www.EmersonProcess.
