|Boilers and Heaters - Improve Energy Efficiency|
|Written by Natural Resources Canada|
|Tuesday, 08 June 2010 16:00|
Boilers and Heaters- Improving Energy Efficiency
Natural Resources Canada ■ Office of Energy Efficiency
ENERGY MANAGEMENT OPPORTUNITIES – TIPS
Approach energy management with an open mind to critically evaluate accepted practices. Some practices may prove to be inefficient. A fresh look or an added awareness, which this chapter aims to supply – combined with imagination and expert assistance – can pay large dividends in reducing energy and costs.
“Energy management opportunities” (EMOs) represents how energy can be used wisely to save money and to limit environmental impacts. This section presents proven ideas that may improve the operation of boiler and heater systems. Choose EMOs from the lists that suit the particular situation and combine them with other energy efficiency measures.
■ The tips for EMOs are presented in three categories. The difference in price between low-cost and retrofit EMOs depends on the size, type and financial policy of the organization. (Housekeeping is the third category.)
■ Due to the variety of possible circumstances, it is impossible to indicate when an EMO will pay for itself. In general, however, retrofit EMOs can be expected to have the longest payback.
HOUSEKEEPING EMOS are energy management actions that are repeated regularly and at least once a year.
■ Run the process equipment using downstream steam (or heating fluid) efficiently by proper production scheduling and maintenance.
■ Try to operate the process equipment using downstream steam (or heating fluid) at capacity.
■ Shut down the equipment in the process using downstream steam (or heating fluid) when it is not needed.
■ Try to stabilize heating demand. To do this, review the schedule for process demand. This will minimize boiler load swings and maximize boiler efficiencies. Try to operate boilers at full load.
■ Maintain good steam quality with a program of regular water chemical treatment and the blowdown regime. Ensure that the feedwater de-aerating equipment and the air vents on the steam piping work properly.
■ Monitor the flue gas combustibles and the combustion excess air regularly. Adjust as conditions change.
■ Check for and eliminate the entrance of unwanted air into the boiler and flue gas exhaust system.
■ Keep burners properly adjusted.
■ Maintain the best operating condition of air and fuel controls.
■ Calibrate measuring equipment and instruments and tune up the combustion control system regularly.
■ Check all the control settings regularly. Check and verify the boiler efficiency regularly.
■ Monitor and compare the boiler performance- related data to standard and targets regularly.
■ Apply routine and preventive maintenance programs to the boiler and heat distribution and condensate collection systems.
■ Inspect the fireside and waterside heat transfer surfaces when the boiler plant is shut down; keep the surfaces clean.
■ Ensure that the fireside anti-fouling equipment works properly.
■ Check the integrity of the steam and condensate network (heating fluid supply and return net- work) and related equipment routinely. Walk through the facility with appropriate detection equipment (e.g. ultrasonic detector, listening rods, pyrometer and stethoscope), looking and listening for steam leaks. Repair the leaks.
■ Set up a steam trap inspection and maintenance program and procedures.
■ Inspect the insulation for waterlogging; locate the source of the moisture (e.g. a leaking pipe) and correct the problem.
■ Replace or repair any missing and damaged insulation and insulation covering.
LOW-COST EMOS are energy management actions that are done once at a reasonable cost.
■ Develop and implement operating procedures and work instructions. Train boilerhouse opera- tors and other employees when necessary. Create an awareness of energy efficiency among all employees.
■ Operate the boiler (heater) at the lowest steam pressure (or heating fluid temperature) that meets the needs of the production process. To do this, the process, plant and equipment may need to be modified.
■ Review whether the type of facility or industry has combustible by-products (e.g. waste hydrogen, oxygen, carbon monoxide, biogas or hydrocarbon streams, or biomass) that could be used as no- or low-cost boiler fuel supplements. Consider using these by-products.
■ Add measuring, metering and monitoring equipment to the boiler and heat distribution systems for fuel, steam, heating fluid, condensate and blowdown flows.
■ Optimize the location of sensors. Make sure that the sensor and control devices can be easily accessed for control and maintenance.
■ Fit controls with locks to prevent tampering and unauthorized adjustment.
■ Consider starting a metering and targeting pro- gram to better manage the use of thermal energy (and other utilities) throughout the facility.
■ Repair, replace or add air vents (e.g. thermostatic air vents).
■ Consider recovering heat from blowdown water. To do this, use flash tanks to generate low-pressure steam from the blowdown (and use it in other heating applications, such as the de-aerator). Use the remaining water in the heat exchanger to preheat makeup water.
■ Overhaul steam pressure-reducing stations.
■ Consider the economics and means of capturing radiation and convection heat from the boiler shell for pre-heating combustion air.
■ Relocate the combustion air intake to a spot where the incoming air has the highest possible temperature year-round.
■ Upgrade the fuel and air controls.
■ Insulate pipes, flanges, fittings and other equip- ment with efficient insulation at an economic thickness. Add insulation where it is inadequate.
■ Review whether the steam and steam condensate recovery network (and heating coils and other steam-using equipment) has proper drainage. This will eliminate water hammer, losses and damage.
■ Shut down the steam and condensate branch system when it is not needed.
■ Look for opportunities to rationalize and streamline the steam and condensate network. Examine current plant-piping drawings, if avail- able, or walk through the facility. First, ensure that the obsolete, unused or redundant piping can be isolated from the rest of the system. Then remove the unnecessary parts.
■ Set up a program for steam trap replacement.
RETROFIT EMOS are energy management actions that are done once at significant cost.
■ Review whether possibilities exist in the facility and industry to eliminate or scale down the use of steam and heating fluid. If so, modify or adopt a new technology or production equipment (e.g. replace pasteurization with sterile filtration and filling). Or supplement heat usage with other sources, such as a ground-source heat pump, solar walls or thermal storage.
■ Replace obsolete boilers with high-efficiency, low-emissions units fitted with new burner technology and heat recovery options suited to the required demand.
■ Upgrade the fuel burner. Consider using fuel direct injection (FDI) technology, for example. A full-time FDI regenerative burner (FFR) reduces NOx emissions by about 90 percent compared with ordinary regenerative burners. The compact FFR burner allows simplification and downsizing, plus a significant reduction in energy consump- tion and a short payback.
■ Install a turbulator in the firetube boiler.
■ Convert the burner from oil to natural gas. (Although this may save more money than energy, it has some operational and environ- mental advantages.)
■ Convert from indirect to direct steam heating, where appropriate.
■ Convert from steam to heating fluid heating, where appropriate.
■ Install an integrated computerized management system for generating and distributing thermal energy.
■ Determine whether a waste product is flared off in the operations (e.g. petrochemical, steel and lime industries). If so, consider using it to preheat boiler combustion air or even to operate a micro-turbine generator.
■ Install equipment to recuperate heat on the flue gas system. This includes economizers, combustion air preheaters and flue gas condensers (indirect or direct contact). If already in place, review its efficiency and consider replacing or upgrading it.
■ Consider alternate uses for the remaining heat in the flue gas. Use it for space heating, process or drying the product or biomass fuel.
■ Consider deploying absorption heat converters (AHC) on the flue gas system.
■ Recover heat from waste streams, such as flash steam. Choose from the many options available. Consider incorporating a heat pump into the system to further boost the energy recovery or integrating the new technology of highly efficient compact heat exchangers (CHE) with other processes.
■ Consider installing a system for closed-loop pressurized condensate return.
■ Hire a qualified contractor to redesign the steam and condensate network to maximize its use. Repipe systems or relocate equipment to shorten pipe lengths.
■ If required, consider moving steam generation units (possibly smaller or new) and delivery closer to the steam-using equipment.
■ Use the correct pipe size. In heating fluid systems, consider the economics of going to increased pipe diameter versus pumping cost and pressure losses.
■ Evaluate the economics of upgrading or adding more insulation. Consider energy cost trends, and consult an unbiased professional. Upgrade insulation cladding.
SAMPLE CHECKLIST FOR AUDITING A BOILER AND HEATER SYSTEM
The following questions will help uncover inefficiencies. Formulate additional questions by the layering technique to get more details.
■ Is the use of steam and heating fluid throughout the facility budgeted? Is it monitored? Are there consumption targets?
■ If so, are the users of thermal energy accountable for its use? How?
■ Are there approved procedures and work instructions governing thermal energy generation, distribution, monitoring and other processes?
■ Have employees learned about the significance of energy and utility conservation, and do they use correct practices?
■ Are boiler and heater operators involved with the efforts to conserve energy and utilities?
■ Are employees aware of how much energy and utilities cost, and how much is being spent for these in the facility? Are they significantly interested in improving the results?
■ Is there a system for communicating to employees the results of efforts to conserve energy and utilities?
■ Are there procedures for shutting off thermal energy-using production equipment and auxiliary production equipment when not in use?
■ Are the above procedures implemented?
■ Is steam or heating fluid produced at tempera- tures or pressures greater than those required by end-user processes, product, plant or equipment?
■ In multiple boiler installations, how is steam demand matched to boiler deployment? How is it done on weekends, during non-production periods and in various seasons?
■ Can a cheaper alternative source for thermal energy be used?
■ Can process by-products be used as an auxiliary fuel or fuel supplement?
■ If natural gas is used, have the costs of uninterruptible versus interruptible supply been evaluated?
■ Is the boiler fitted with dual capability to use natural gas or fuel oil to take advantage of interruptible gas supply contracts?
■ Are heated oil tanks and associated piping adequately insulated?
■ Is the external insulation for the above items watertight?
■ Is oil heated at the correct temperature?
■ Is solid fuel (e.g. biomass) protected against rain? Is it dried?
Boilers and steam distribution
■ Is the flue gas free of combustibles?
■ Is the boiler efficiency checked on a regular basis?
■ Is a proper method for determining boiler efficiency being used?
■ Is the efficiency acceptable for the type of boiler and fuel?
■ Is the burner operating in the “zone of maximum combustion efficiency”?
■ Are the heat losses of the boiler and system known and quantified?
■ Is the flue gas checked for combustibles, carbon monoxide and oxygen content on a regular basis? Is the content within an acceptable range?
■ How is the excess combustion air managed? How frequently?
■ Can unwanted air get into the boiler and the flue stack?
■ What type of air or fuel control is used? How is it maintained?
■ What type of equipment is used for controlling and monitoring the system? What instruments are used?
■ Where is the combustion air intake located?
■ Is the combustion air preheated? If so, how?
■ Are the NOx levels in the flue gas known and monitored? Are they within an acceptable range?
■ What are the flue gas temperatures at various boiler loads? Are they monitored?
■ Is heat being recovered from flue gas? What type? How efficiently?
■ Is there any evidence of soot buildup on the fireside surface of the boiler?
■ Is there a program for inspecting and removing soot and scale from heat transfer surfaces of the heater and boiler? From process equipment?
■ Is the flame in the combustion chamber bright and clear? Does it fill the combustion chamber without encroaching?
■ What is the blowdown rate, and is it at the level recommended by water treatment specialists? Is it based on the content of dissolved solids (DS) in the boiler water? Have the levels of DS content been calibrated to conductivity?
■ How is the blowdown rate controlled?
■ Is there a system for recovering heat from the blowdown?
■ Is there redundant, oversized or undersized steam piping that causes heat losses? Is there an inspection program for it?
■ Are steam lines, flanges, valves and condensate lines adequately insulated? Is the insulation dry and protected against water ingress?
■ Is steam or condensate leaking?
■ Is the makeup water preheated? If so, how?
■ Is the condensate return rate adequate? Has it been verified?
■ Is the correct type of steam traps for the application being used?
■ Is there an adequate maintenance program for inspecting, repairing and replacing steam traps? How many of the traps are faulty?
For more information or to receive additional copies of this publication, write to:
Canadian Industry Program for Energy Conservation c/o Natural Resources Canada Office of Energy Efficiency, 580 Booth street, 18th Floor, Ottawa ON K1A 0E4
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