Steam System

Steam, used in most significant amounts in chemical pulping, bleaching, evaporation, and drying processes, is the biggest energy carrier used in a pulp and paper mill and fuel input to the boilers is usually the largest share of the energy consumption. Consequently, improving the energy efficiency of the steam system holds a significant potential for reducing the energy consumption in a mill.

Steam system details may vary from mill to mill. In general, however, the system has two main parts: the boiler and the steam distribution system. There are several measures that should be considered for these parts. In improving the energy efficiency of steam systems, it is essential to dopt a systems approach and optimize the system by assessing optimization opportunities both with the demand (i.e., end uses) and the supply of steam.

Steam SystemTechnologies & Measures

Technology or MeasureEnergy Savings PotentialCO2 Emission Reduction Potential Based on LiteratureCostsDevelopment Status
Boiler Process ControlAn audit in a a mill in the US identified an opportunity to save $475 000 (2002 dollars) annually with the optimization of the boiler operations with a control system. Estimated payback time was less than 6 months (Kramer et al., 2009. p.45)Commercial
Improved steam distribution systems insulationThe U.S. DOE estimates that the installation of removable insulation on valves, pipes, and fittings can reduce steam system energy use by 1-3% (U.S. DOE 2006c).Case studies from the U.S. pulp and paper industry indicate that the payback period for improved insulation is typically less than one year (IAC 2008). Commercial
Reduction of Flue Gas QuantitiesBoiler energy consumption can be reduced by 2 to 5% (Kramer et al., 2009. p.45).Commercial
Insulation maintenanceAs part of an energy use and energy efficiency opportunities case study of ten different pulp and paper mills in Illinois, it was shown that installing or improving insulation on pipes and valves could save (on average) over 3,800 GJ (Chimack et al. 2003).The U.S. DOE estimates that (as of 2002) roughly half of U.S. pulp and paper mills could significantly benefit from insulation improvements and installation, and that these mills could reduce their boiler fuel use anywhere from 3% to 10% if such improvements are pursued (U.S. DOE 2002b).Commercial
Reduction of Excess Air

US flag U.S. DOE estimates that U.S. pulp and paper plants could reduce boiler fuel use by around 2.3% by reducing excess air (Kramer et al., 2009. p.45).

US flag An audit in a 1 000 tpd kraft mill plant found that by fine-tuning the flue gas oxygen concentrations so as to reduce them from 8–12% to 6–7%, significant amounts of fuel can be saved.

US flag Another audit in another mill identified an opportunity to save 16 350 GJ/y of energy by by adjusting boiler oxygen trim controls to lower the oxygen levels to between 2.5-3% (Kramer et al., 2009. p.46),

US flag Corresponding kraft mill could save around $ 70 000 due to reduced fuel consumption;

US flag Saving 16 350 GJ/y of energy could save the compay $118 000/y (Kramer et al., 2009. p.46),

Commercial
Steam trap improvementCommercial
Improved Boiler InsulationSavings of 6-26% can be achieved, if improved insulation is combined with improved heater circuit controls.Commercial
Steam trap maintenanceEnergy savings for a regular system of steam trap checks and follow-up maintenance is conservatively estimated at 10% (Jones 1997; Bloss et al. 1997).Several industrial case studies suggest that investments for repair or replacement steam traps are very low, resulting in a payback period of only a few months or less (IAC 2008).Commercial
Boiler maintenanceThe lack of boiler maintenance can end up costing a steam system up to 30% of initial efficiency over two to three years (Galitsky et al. 2005a). On average, the energy savings associated with improved boiler maintenance are estimated at 10%.Improved maintenance may also reduce the emission of criteria air pollutants.Commercial
Steam trap monitoringEmploying steam trap monitoring has been estimated to provide an additional 5% in energy savings compared to steam trap maintenance alone (Galitsky et al. 2005a). Employing steam trap monitoring has been estimated to have a payback period of around one year (Galitsky et al. 2005a). Commercial
Condensate returnThe U.S. DOE estimates that this measure can lead to a 1.5% reduction in boiler fuel use at U.S. pulp and paper mills, at an average payback period of around 15 months (U.S. DOE 2002b). In a specific example, the U.S. DOE reports that a large specialty paper plant reduced its boiler makeup water rate from about 35% of total steam production to less than 20% by returning additional condensate; annual savings were around $300,000 (U.S. DOE 2004a).Commercial
Leak repairThe U.S. DOE estimates that repairing leaks in U.S. pulp and paper mill steam distribution systems could lead to fuel savings of around 2% (U.S. DOE 2002b). Case studies of U.S. pulp and paper mills in the IAC database suggest a payback period for this measure of less than one year (IAC 2008).Commercial
Minimizing boiler blow down Case studies from the pulp and paper industry suggest that automatic blow down systems can have a payback period of just six months (Focus on Energy 2006a). The U.S. DOE estimates that improving blow down practices can lead to annual boiler fuel savings of around 1.1% (U.S. DOE 2002b).Commercial
Flash steam recoveryWhere feasible, this measure can be easy to implement and can save considerable energy.The potential for this measure is site dependent, as its cost effectiveness depends on whether or not areas where low-grade heat is useful are located close to steam traps.Commercial
Blow down steam recoveryExamples of blow down steam recovery in the pulp and paper industry suggest a payback period of around 12 to 18 months for this measure (Focus on Energy 2006a). The U.S. DOE estimates that the installation of continuous blow down heat recovery systems can reduce boiler fuel use by around 1.2% (U.S. DOE 2002b).Commercial
Flue gas heat recoveryTypically, one percent of fuel use is saved for every 45°F (25°C) reduction in exhaust gas temperature (Ganapathy 1994). A conventional economizer would result in savings of 2-4%, while a condensing economizer could result in energy savings of 5-8% (Gardner 2008). However, the use of condensing economizers is limited to boilers using clean fuels due to the risk of corrosion.The U.S. DOE estimates that the installation of boiler feedwater economizers can reduce boiler fuel use by around 3.5% (U.S. DOE 2002b).Commercial
Burner replacementAs part of an energy use and energy efficiency opportunities case study of ten different pulp and paper mills in Illinois, it was shown that improving boiler combustion efficiency, using blow down steam energy rather than live steam to preheat makeup feedwater, and installation of stack economizers could save (on average) over 9,500 GJ per year (Chimack et al. 2003).For example, the payback time for a new burner that provides a boiler efficiency improvement of 2% will be around one year (U.S. DOE 2004a). In one example from the pulp and paper industry, replacing circular oil burners with more efficient parallel throat burners with racer type atomizers had a payback of approximately one year (Focus on Energy 2006a). The U.S. DOE estimates that upgrading burners to more efficient models or replacing worn burners can reduce the boiler fuel use of U.S. pulp and paper mills by around 2.4% with a payback period of around 19 months (U.S. DOE 2002b).Commercial
Steam distribution controlsCommercial

Steam System Publications

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