Boiler Burners : In Depth: Does Your Waste to Energy Firm Have Money to Burn?

Throughout the different thermal processes in a waste to energy plant, energy is lost due to equipment inefficiencies as well as mechanical and thermal limitations. Companies find that over time burner settings will drift due to component wear, temperature, dirt, soot and leaks. This drifting can ultimately affect an organization’s fuel usage, equipment efficiency, and product quality.

Understanding how energy is used and wasted can help operators identify ways to improve efficiency. Consider these three ways boilers and their burners impact a company’s bottom line:

Substantial savings can be achieved if your boiler, including the burner, has a regular maintenance schedule that is based on operating conditions.

Like a carburettor in your favourite old car, burners are typically tuned in the summer and winter months. Tuning optimises the fuel/air ratio for the ambient air, warm air during the summer months and cool air during colder winter months so that the boiler operates more efficiently while maintaining safety. The burner tuning procedure is complex and exacting, since every 2% increase in O2, can result in a loss of 1% in efficiency. An improperly tuned burner is just as bad as an out of tune burner.

To fully reap financial benefits, it is very helpful to work with a knowledgeable, experienced and qualified industry expert. A tighter control of the air/fuel ratio, results in a better control of the combustion reaction and its efficiency. On average, companies with industrial boilers that have regular tuning schedules can see a 1% - 2% fuel savings.

A maintenance schedule that includes regular boiler cleanings can help avoid costly stress on a company’s boiler. Without regular cleanings, heavy sooting will occur due to incomplete combustion of the fuel air mixture of the burner. Buildup of this heavy soot will start to insulate the inside of the boiler resulting in heat transfer efficiency becoming less and less as more and more heat starts to escape through the boiler stack.

Damaging soot accumulation will also generate hot spots within the boiler which can eventually lead to boiler cracks, stress fractures, ligament fissures and reduction of heat transfer in the boiler. The devastating result can be exceedingly costly repairs or purchase of a new unit.

To decrease the air pollution produced by boilers (carbon monoxide, hydrochloric acid, mercury, and trace amounts of other heavy metals) in many countries boiler and burner tune up requirements are regulated.

For example, in the US, under Environmental Protection Agency (EPA) regulations, most companies operating an industrial, commercial or institutional boiler must meet compliance - National Emission Standards for Hazardous Air Pollutants for Area Sources (NESHAP) 40 CFR part 63. Without these mandatory tune ups, companies can face both civil and criminal penalties that could include daily fines and even imprisonment.

All the issues listed can contribute to a less-than-optimal use of fuel, energy and equipment, in addition to increases in operating costs.

The burner is really at the heart of boiler efficiency, if you don't have a good burn, and decent heat transfer, it seriously limits operations. As a result, top priority should go to keeping an organization’s burner tuned by a knowledgeable expert. The damage that can be caused by an improperly tuned burner is almost as great as that of a totally untuned burner, and in a fuel-rich environment could lead to an explosion.

Whether you tune your boiler and burner regularly for compliance reasons, cost efficiency, or both, keeping them tuned should be an integral part of any industrial, institutional and commercial maintenance program.

In waste to energy plants the intense heat which is required for the combustion process, the fire wears away the 'fire brick' or Refractory Lining. Refractory Removal is essential for inspection, repair, maintenance and replacement. Dan Szynal, Vice President of Engineering and Technical Service for the Plibrico Company explains the importance of anchor design.

It is estimated that up to 40% of refractory lining failures can be attributed to a problem with the design of the anchor system or improper installation. This is a significant number. When designing a refractory lining for an industrial application, anchor design becomes one of the most important factors in creating a robust lining that is supported properly. In particular, the tips of the anchors experience the highest temperatures because they are closest to the hot face and thus become an important consideration.

Anchors have several functions. They hold the refractory to the wall to keep it from falling in. They also prevent wall buckling due to the internal thermal stresses created by high temperatures. And, to a lesser degree, anchors can also help support the load of the refractory weight.

To create a monolithic refractory lining that is properly supported and maximises service life, here are three important metallic anchor tips you need to know.

For refractory linings in which metallic anchor systems are used, refractory engineers and designers almost always use Class III austenitic stainless-steel anchors of various qualities. The typical grades of stainless steel used are AISI 304, 309, and 310. These contain chromium and nickel to provide the best corrosion resistance and ductility at high temperatures. For some applications in which temperatures are more extreme, and the use of ceramic tile anchors is not practical for various reasons, AISI 330 and even Inconel 601 is sometimes used. These anchors have higher nickel content for superior oxidation resistance and tensile strength at temperatures of 2000°F or higher. Inconel 601 gives the added advantage of good resistance to both carburisation and sulfidation in extreme applications.

Anchor sizing for a refractory lining depends on the refractory thickness and number of components. Some designers use the practice of sizing the anchor height to be 75%-85% through the main dense castable or gunned lining. Other rules of thumb used in the industry dictate that the anchor tip should be no more than two inches from the hot face of the refractory for thicker lining designs greater than 6"-7".

For refractory applications, it is useful to know the temperature gradient through the refractory lining, from the hot face to the cold face, to choose the proper anchor size so that one doesn’t exceed the temperature limit of the alloy being used. To help calculate the correct temperatures at different points in the refractory lining, many industry professionals will use a heat loss calculator/estimator. Using a heat loss calculator/estimator, one can choose the proper anchor height by determining the anchor tip temperature it will experience. There are numerous heat loss applications that can estimate the cold face of a furnace lining given the input conditions of a thermal unit.