Investors | About Us | News & Events | Careers Industries Products Contact Us Energy Tips Archive September 2015 What is the role of monitoring in optimizing a dryer section? Optimizing a dryer section begins with monitoring the dryer section operation and developing a baseline for dryer section performance. The baseline can be compared to the performance of similar machines producing similar grades. This baseline can also be used to evaluate the impact of changes made on the machine. Improvements, however, require an active program that follows and acts on the data. Daily production meetings should include a review of energy efficiency readings. This will help to identify losses as they occur. For example, an increase in steam going to a condenser may indicate the differential steam pressures are too high. A vent valve opening up may indicate a thermocompressor is running in a choked flow condition. An increase in the dryer steam flow (per ton of product) may indicate the exiting press moisture is increasing and it is time to change one of the press felts. An increase in steam pressure to the air heaters may indicate air filters are plugged and need to be replaced. Again, the first step is monitoring. The next steps involve acting on the results. August 2015 Where do you start in optimizing a dryer section? The dryer section consumes large amounts of energy and it can have a dramatic impact on both sheet quality and profitability. The drying process, like other papermaking unit operations, is a complex matrix of interacting systems: Pocket ventilation, steam system, drive system, tail threading, sheet handling, energy recovery, and fabric conditioning, guiding, and tensioning. A good way to start an evaluation of the dryer section is to contact a drying systems supplier, consultant, or engineering firm for a dryer audit. A professional dryer audit should include a complete set of dryer section measurements, an analysis of equipment sizing, recommendations for operational improvements, recommendations for equipment upgrades, lists of short-term and long-term improvement projects, and an analysis of the expected return for each project. Typical returns come from energy savings, increased drying capacity, reliable dryer drainage, reliable dryer drainage equipment, improved dryer section runnability, and enhanced drying uniformity. A comprehensive report identifies improvement opportunities and quantifies the associated benefits. July 2015 What is the correct operating differential pressure for a dryer section? The correct operating differential pressure for maintaining dryer drainage depends on a number of parameters. Some of the more important variables are: dryer section steam pressure, steam condensing rate, type of dryer syphon (rotating, stationary, or scoop), syphon pipe sizes, machine speed, and dryer diameter. When it comes to setting the operating differential pressure, unlike the Ron Popeil 4000 rotisserie, operators cannot just "set it and forget it". The operating differential pressures must be adjusted to reflect changes in operating conditions that come with start-ups, shut-downs, grade changes, and sheet breaks. Operators can make these changes manually, or they can use a supervisory control system, to make the changes automatically. June 2015 Is it important that differential pressure transmitters be calibrated? Proper calibration of instrumentation is at the heart of any efficient dryer section operation. If a process parameter cannot be properly measured, it cannot be properly controlled. Differential pressure transmitters are particularly important. Dryer drainage depends on it. Dryers with rotary syphons will flood if the differential pressure is not high enough and they will pass excessive amounts of blow-through steam if the differential pressure is too high. Even with modern stationary syphons, accurate differential pressure measurement is very important. Only 3-4 psi differential pressure is needed to drain the dryers with a stationary syphon, but with a measurement error of only 2 psi, the blow-through flow will easily be either inadequate or excessive. It does not end there, the differential pressure transmitters may be properly calibrated, but the pressure sensing lines may not be delivering the right pressure to the transmitter. Over half of the dryer sections surveyed by Kadant Johnson had sensing lines that were improperly designed, installed, and maintained. May 2015 Does the grouping of dryers affect energy efficiency? The grouping of dryer cylinders in separate steam groups does not directly increase or decrease the amount of energy required to dry the paper web. The grouping of dryers does, however, have a direct effect on the design and ultimately on the performance of the dryer steam system. In a thermocompressor steam system, for example, each thermocompressor must be sized to match the number of dryers in the section, their operating steam pressures, the differential steam pressures, and the resulting blow-through steam flow. In a cascade steam system, the down-stream dryer groups must be sized to use the blow-through steam flows from the up-stream dryer groups. The last of the steam groups must also be properly sized so that its blow-through steam is either used in a low-pressure process or low enough in quantity to be discharged to a condenser. Without a proper grouping of dryers, the steam energy will be lost, either through vent valves to the atmosphere or to condensers. April 2015 What is the difference between sensible heat and latent heat? "Sensible" heat is energy that results in a change in temperature, that is, energy transfer that can be sensed. "Latent" heat is energy that is required for a change in state, for example, to evaporate water without any change in the water temperature. Latent heat is also known as "heat of evaporation" or "heat of condensation". When drying paper, some of the drying energy is required to increase the temperature of the sheet, without evaporating any water. This is called sensible heating. The majority of the energy required for drying paper is the energy required to evaporate the water. This is called the latent heat. It takes about 30 Btu (British Thermal Units) of energy to increase the temperature of one pound of water from 182°F to 212°F. It takes 970 Btu to evaporate that same pound of water with no change in its temperature. The least amount of energy is required to dry the paper when the wet web is not over-dried (that is, when it is not over-heated) and when the amount of water that must be evaporated is minimized, for example, by having higher exiting press dryness or a higher reel moisture content March 2015 Why are dryer surface temperatures measured in a dryer study? The surface temperature of a dryer is a good indicator of dryer performance. The temperature of the surface is compared to the temperature of supply steam (the "saturation" temperature that corresponds to the dryer steam pressure). The difference between the dryer surface temperature and the steam temperature is an indication of heat transfer efficiency from steam through the condensate in the dryer, the cast iron dryer shell, contamination on the inside and outside of the dryer, and any other resistance between the steam and sheet. Interpretation of these results, however, requires some care. High dryer surface temperatures, for example, can be the result of very good heat transfer from the steam to the dryer shell, but they can also be the result of poor thermal contact between the dryer shell and the sheet. When used in conjunction with other measurements (machine speed, trim width, grade, steam pressures, condensing load, fabric tensions, etc.), the dryer surface temperature measurements can provide valuable information on areas for potential improvement. February 2015 What is the recommended frequency for dryer inspections? There may not be pressure vessel code, local jurisdictional, or other regulatory requirements for periodic dryer inspection, but it is a good practice to formally inspect dryers every five years. To make this process more manageable, mills and their insurance carriers will often adopt a program in which 20% of the dryers are inspected each year so that all dryers are inspected on a five-year cycle. These inspections include magnetic particle testing of dryer heads, ultrasonic testing of head bolts, dryer shell thickness measurements, acoustic emissions examination, and external and internal visual inspections. Internal visual inspections should identify grooves in the shell, erosion under syphon shoes, loose dryer bars, loose dryer balance weights, visible casting flaws, and erosion or damage to syphon piping. Eroded syphon shoes, eroded syphon elbows, and leaks past syphon flange gaskets can lead to poor condensate evacuation, increased operating differential pressures, and high blow-through steam flows. These in turn reduce the energy efficiency of the drying process. January 2015 What is the optimum operating tension for a dryer fabric? It depends. Dryer fabrics hold paper in tight contact with dryer surfaces to increase the drying rate and heat transfer uniformity. On some paper machines, dryer fabrics are also used to drive dryer cylinders. Dryer fabrics can also reduce the cross-directional shrinkage of the paper web. Despite these positive effects, there is a point of diminishing return. Excessive tension can damage the fabrics and paper machinery with no practical gain in drying capacity, drivability, sheet handling, or sheet restraint. Fabric tensions should never exceed those recommended by the fabric supplier or the equipment manufacturer. That said, the minimum fabric tension is about 4 pli and felt tensions in the range of 10-20 pli would normally give high drying rates, stable fabric guiding, and good machine runnability. Slightly higher values may be required on machines with runnability components such as blow boxes and vacuum boxes. December 2014 Is a dryer fabric cleaning system required for high energy efficiency? Clean dryer fabrics do not directly increase or decrease the amount of energy required to dry the paper web. However, dryer fabrics that have a lot of build-up of fiber, filler, and stickies will reduce the uniformity of heat transfer, the effectiveness of the dryer pocket ventilation system, and sheet runnability. These lead indirectly to more demands on the cross-machine profiling devices, reduced drying capacity, and more sheet breaks. These all result in reduced energy efficiency. Fabrics can be cleaned by a number of methods, either during a shut-down or on-the-run. On-the-run devices use a series of high-pressure water jets and an integral system for capturing and removing the debris cleaned off of the dryer fabrics. November 2014 How does basis weight affect energy consumption? In general, higher basis weight grades cost more to produce. This is not only because of higher fiber cost, but also because of higher energy costs. More water must be evaporated from a heavy weight sheet than from a lighter weight sheet. If sheet properties can be maintained with a lower basis weight, significant savings in both fiber cost and energy cost can be achieved. For example, if a roll press is replaced with an Extended Nip press, the outgoing press moisture is reduced and sheet caliper is maintained and in some cases increased. This results in a stronger sheet, one that can achieve the strength specifications with less fiber and less energy for production. This is a double-count win. October 2014 Does the type of rotary steam joint affect energy consumption? Yes, the type of rotary joint does affect the consumption of energy. Older style rotary joints, self-supported joints and many lug-supported joints, use internal steam pressure to apply load to the carbon sealing ring. It takes high torque to rotate these "pressure joints", particularly when the steam pressure is high. Modern compensated steam joints, such as the Kadant Johnson PTX® steam joint, require much less torque. For example, the drive power for a machine running at 1750 fpm with (80) 60" diameter dryers could be reduced by 80 hp simply by converting from pressure joints to PTX steam joints. At an electrical energy cost of $0.07 per kWhr, this would be a savings of over $35,000 per year. The elimination of steam leaks and rotary joint maintenance makes the savings even larger. 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