We are committed to burning fossil fuels. Our society depends on the energy produced from fuels; be it from coal-fired electrical generating stations or wood stoves for heating our homes. We are learning that there are significant costs associated with the combustion processes that meet our demand for energy. The monetary cost is immediately evident to building owners and industrial plant managers when paying their fuel and electricity bills. The less obvious cost is the environmental effects. All combustion processes produce emissions that cause smog, acid rain, and global warming. Fortunately reducing the monetary costs and emissions can go hand in hand. Improving combustion processes and efficiencies reduce the amount of fuel consumed, which means fewer emissions into the atmosphere and less dollars for overall energy costs!
The majority of combustion for industrial and heating applications occurs in boilers or heaters. This guide is addressed to owners and operators of boilers and heaters and is intended as a simple, yet informative, overview of the combustion process and its emissions and how efficiencies can be improved. It covers such topics as boiler efficiency, NOx emissions, air and fuel control, and energy conservation measures. It also includes accounts of successful projects that, through thoughtful consideration and use of current technology, have reduced operating costs and reduced the load on the environment.
Introducing The Comforts and Concerns of Combustion
What are the products of combustion, and why are we concerned about them?
Getting the Most for your Fuel Bill
Practical considerations about the design and operation of boiler plants, such as properly selecting boiler energy sources: steam or water boilers or even cogeneration systems. It includes discussions of piping systems and their energy losses and the energy savings that can be addressed under general boiler plant operation.
Benefits of Better Burning
T he basics of combustion and a useful theoretical explanation of boiler efficiency. (A detailed discussion can be found in Appendix 1). A number of efficiency factors are decided at the design stage: fuel type, boiler size, and heat recovery. Once specified, these particular efficiencies are fixed and can only be improved with further capital investment. Operating efficiency can be monitored by measuring the flue gas oxygen concentration and temperature and, as discussed in Chapter 4, can be improved by properly adjusting the air/fuel ratio.
Air/Fuel Control – Getting There and Staying There
Good air/fuel ratio control is the principal means of increasing boiler efficiency, once the equipment is installed. Its primary function is to ensure there is always sufficient air to completely burn all the fuel. Combustion with less air than required can cause boiler explosions. However, more air than necessary reduces efficiency. The goal when optimizing the air/fuel ratio is to reduce the air to minimum without entering areas of unsafe operation. The chapter presents a range of air/fuel control techniques, from the simplest to advanced strategies applied to large boilers. It also discusses automatic oxygen control, called oxygen trim, which continuously optimizes the air/fuel ratio (usually used on the largest boilers). Adjusting the burners for optimum operation must be done for the initial boiler commissioning and should be repeated on a regular schedule afterward. For the information of owners and operators when requesting burner adjustments, a procedure for adjusting air/fuel is given in this chapter. In addition a sample specification is given for purchasing high efficiency (and Low-NOx) burners.
Understanding Atmospheric Emissions
Depending on the fuel, different atmospheric emissions are generated in varying amounts from the combustion process. A general overview of emissions and their effects is discussed in Chapter 5. Over the past decade, burner designs have seen large improvements to reduce the nitrogen oxides (NOx) that are associated with smog and acid rain. The chapter presents the cause of NOx and techniques for reducing NOx combustion emissions. Some NOx reduction technologies currently available are presented in Appendix 2.
Right with the Regulations
The regulations associated with combustion and its emissions are discussed in Chapter 6. The discussion focuses primarily on NOx and includes sources for further investigation of detailed regulations within the Ontario jurisdiction. For an owner/operator of boiler and combustion systems, improving operating efficiencies and reducing emissions can be had in many areas. However, as discussed in the guide, particular attention should be paid to efficiency and emissions when selecting equipment. This is especially true when replacing existing equipment. It is the ideal time to validate equipment selection, rather than simply replacing with the same equipment, using the past operating records and by system testing to confirm actual operating loads. With increasing regulatory attention to environmental emissions, this is also the time to install combustion equipment that will meet current and proposed future emission limits.
Three case studies of projects resulting in energy and emission reductions are included to show what is possible. They reflect the major topics discussed in the guide. One project reduced costs and emissions by installing new, efficient, properly sized boilers with heat recovery and Low-NOx burners. Another achieved the same result using high efficiency, direct contact water heaters and the third selected cogeneration. Each project demonstrates that, with knowledge and effort, the amount of fuel we burn, and the associated costs and emissions, can be reduced.
Measuring Boiler Efficiency
Maintaining optimum boiler efficiency not only minimizes CO2 emissions, it conserves
fuel resources and saves money. One might therefore expect boiler efficiency to be
routinely monitored, especially in larger heating and industrial steam plants. Usually,
however, it is addressed only once or twice a year, by a technician setting up the
automatic controls, and whose focus is more likely to be on safe, trouble-free operation
than on optimum efficiency.
Some Proprietary Low-NOx Burners
Manufacturers of boilers and burners have worked the various NOx reduction technologies into new equipment designs that are proving to be very successful in reducing emissions. Some have developed low-NOx burners that can be retrofitted to existing boilers and heaters; others have designed complete systems, integrating burner and furnace design for best effect.
References and Links for Additional Information