Controlled cavitation can increase recovery efficiency.Everyone knows the sound of banging water pipes. Laymen call it "water hammer Water hammer The propagation in a liquid of an acoustic wave that is caused by a rapid change in fluid velocity. Such relatively sudden changes in the liquid velocity are due to events such as the operation of pumps or valves in pipelines, the collapse of ," and scientists call it "cavitation cavitation Formation of vapour bubbles within a liquid at low-pressure regions that occur in places where the liquid has been accelerated to high velocities, as in the operation of centrifugal pumps, water turbines, and marine propellers. ." Several years of research and pilot projects have shown that the "destructive force" of cavitation can have useful purposes. A liquid passing through a Shockwave Power[TM] Reactor (SPR spr Spring SPR Strategic Petroleum Reserve SPR Surface Plasmon Resonance SPR Suomen Punainen Risti SpR Specialist Registrar (UK doctor who supports a consultant) SPR Society for Psychical Research SPR Stop Prisoner Rape ) undergoes "controlled cavitation." In an SPR, microscopic cavitation bubbles form. When they collapse, heat transfers to the liquid without heat transfer surfaces or combustion. No scaling occurs between liquid and metal. Adding a gas, powder, or other material to a liquid cavitation causes the additive to disperse to almost microscopic size. This increases the surface contact area between materials and maximizes the process. SPR technology offers benefits for heating liquids by preventing scale accumulation and by promoting mixing of liquids with gases (two phase fluids), powders, and other liquids at the microscopic level to increase mass transfer rate. Chemical recovery from black liquor Black liquor is a byproduct of the Kraft process, (also known as Kraft pulping or sulfate process) during the production of paper pulp. Wood is decomposed into cellulose fibers (from which paper is made), hemicellulose and lignin fragments. is an essential part of most paper mills. Because of large capital investments, operating efficiency is critical. Development of three black liquor applications helps mills achieve these goals. INCREASING EVAPORATOR EFFICIENCY If evaporators are running inefficiently because of scale buildup, black liquor preheating by oxidation should eliminate this problem. Preheating a liquor before the "effect" where the scaling is occurring has shown elimination of as much as 98% of the scale. This increases uptime and significantly reduces or eliminates expensive hydro blasting, boil-outs, and mini-washes. [ILLUSTRATION OMITTED] [ILLUSTRATION OMITTED] A SPR has had successful use in earlier tests to heat black liquor without scaling (see Frederick, et al in "Additional Resources"). In contrast to a standard heat exchanger heat exchanger Any of several devices that transfer heat from a hot to a cold fluid. In many engineering applications, one fluid needs to be heated and another cooled, a requirement economically accomplished by a heat exchanger. , the SPR does not require a hot surface. Instead cavitation generates heat directly in the black liquor. Another method to heat black liquor indirectly is partial oxidation In chemistry, a partial oxidation reaction occurs when a substoichiometric fuel-air mixture is partially combusted in a reformer, creating a hydrogen-rich syngas, which can then be put to further use, for example in a fuel cell. . Because sulfide oxidation is an exothermic exothermic /exo·ther·mic/ (-ther´mik) marked or accompanied by evolution of heat; liberating heat or energy. ex·o·ther·mic or ex·o·ther·mal adj. 1. reaction, liquor temperature will increase as oxidation occurs. Partial oxidation of kraft liquors can combine with controlled cavitation in the SPR to increase the economic efficiency of heating. Replacing electricity with oxygen reduces the cost of heating the liquor. A recent project used a pilot SPR unit to mix oxygen in black liquor for rapid oxidation to heat the liquor. The purpose of this work was to evaluate the fouling tendency of SPR-heated black liquor in conventional heat exchangers. Several trials used the Institute of Paper Science and Technology (IPST IPST Institute of Paper Science and Technology, Inc. IPST Internet Professional Sales Training ) annular-flow heat transfer fouling test cell (ATC ATC Air Traffic Control ATC Average Total Cost ATC Certified Athletic Trainer ATC At the Center (Hartford, Maine retreat center) ATC Applied Technology Council ATC All Things Considered ) to simulate the thermal environment in a live-steam-heated black liquor evaporator. Precise control of liquor conditions and sensitive instrumentation in the ATC allowed measurement of the rate of fouling due to calcium carbonate calcium carbonate, CaCO3, white chemical compound that is the most common nonsiliceous mineral. It occurs in two crystal forms: calcite, which is hexagonal, and aragonite, which is rhombohedral. deposition. The calculated fouling rates from two baseline tests with no SPR treatment were 0.33-0.67 mm/hr. Partial oxidation treatment using the SPR reduced the fouling rate to 0.00-0.07 in three trials. [FIGURE 1 OMITTED] Baseline tests performed with untreated liquor determined the rate of fouling with a 20[degrees]C temperature differential between the electrically-heated surface in the ATC and the circulating black liquor. The dark line in Fig. 1 shows the calculated heat transfer coefficient The heat transfer coefficient is used in calculating the convection heat transfer between a moving fluid and a solid in thermodynamics. The heat transfer coefficient is often calculated from the Nusselt number (a dimensionless number). for an unoxidized mill liquor with 44% solids content. The decrease during the first 60 minutes indicates that this liquor has a high propensity to form scale. Other tests performed using the same initial batch of black liquor involved initial heating to more than 130[degrees]C by partial oxidation in the SPR during transfer into the ATC apparatus. In one test, the liquor was at the treatment temperature while testing in the ATC. As expected, the temperature differential of 2[degrees]C resulted in very little change in heat transfer coefficient over several hours. In this case, preheating reduced the driving force for calcium compounds to deposit on the heat transfer surface. [FIGURE 2 OMITTED] [FIGURE 3 OMITTED] In another test, the liquor cooled as it entered the ATC flow loop after SPR heating to 130[degrees]C. This ATC test used the same 20[degrees]C temperature differential of the base line test. The line plot in Fig. 1 shows that no significant scaling occurred during four hours. This result implies that partial oxidation treatment in the controlled-cavitation mixer imparted a sustained change to the black liquor. Based on research at IPST by Frederick and Grace (see Additional Resources), a reasonable conclusion is that heating the liquor above the maximum temperature encountered in the subsequent test may alter its chemistry and greatly reduce the fouling tendency of the liquor. INCREASING THROUGHPUT Using similar oxidation chemistry when the recovery boiler Recovery boiler is the part of Kraft process of pulping where chemicals for white liquor are recovered and reformed from black liquor. In the process lignin of the wood, bound in black liquor at this phase, is burned and heat generated. is steam limited, the black liquor heat value reduction application allows a mill to efficiently increase boiler production up to 7% using a small, skid-mounted SPR. All this is possible without additional storage tanks or producing non-condensable gasses. If a mill needs to address an environmental issue regarding sulfur emissions, the black liquor polishing application could be very economically viable. [Na.sub.2]S can decrease to non-detectable levels of less than .01 grams per liter. This is far below what most technologies can deliver efficiently. The SPR can be beneficial in many areas of the recovery cycle. These include scale-free heating, heating by oxidation, polishing, and HVR HVR Hover HVR Haveri (India) HVR Havre, MT, USA - City County (Airport Code) HVR Home Video Recorder HVR High Volume Retailer HVR High Voltage Relay HVR High Volume Repetitive . WHAT YOU WILL LEARN * How SPR technology offers benefits for heating liquids. * How this technology can improve recovery boiler throughput. ADDITIONAL RESOURCES * Frederick, J., Armstead, D., Lien, S., Schmidl, W., and Kazem, B., "Economic Benefits of Utilizing Controlled Cavitation Technology for Black Liquor Oxidation and Heating," Proceedings of the 2001 International Chemical Recovery Conference. * Frederick, W. J., and Grace, T. M., "A Study of Evaporator Scaling: An Evaluation of Thermal Deactivation de·ac·ti·vate tr.v. de·ac·ti·vat·ed, de·ac·ti·vat·ing, de·ac·ti·vates 1. To render inactive or ineffective. 2. To inhibit, block, or disrupt the action of (an enzyme or other biological agent). 3. ," Project 3234, Report 4, The Institute of Paper Chemistry, Atlanta, GA, November 15, 1977. * Hydro Dynamics Web site: www.hydrodynamics hydrodynamics: see mechanics. Hydrodynamics The study of fluids in motion. The study is based upon the physical conservation laws of mass, momentum, and energy. .com. ABOUT THE AUTHOR Rockwell Holland is vice president of operations for Hydro Dynamics, Inc., Rome, Georgia Nestled in the foothills of the Appalachian Mountains, Rome is the largest city in and the county seat of Floyd County, Georgia, United States. It is the principal city of the Rome, Georgia Metropolitan Statistical Area which encompasses all of Floyd County. , USA (Web site: www.hydrodynamics.com). Contact the author by email at rholland@hydrodynamics.com. [ILLUSTRATION OMITTED] |
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