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From long ago to today, combustion and furnaces are the heart of our society. The combustion process and industrial furnaces play a significant role in our life. Furnaces are used to produce everything we need today, such as food and drink. Types of burners in the furnace are divided into different categories based on their applications and fuel consumption. Ceramic or metallurgist processes, heat treatment, melting, and casting furnaces for metals and non-metals or melting for glass industries are categorized. Gas furnace burners and oil furnace burners are other specifications for industrial categorization. Furnaces need industrial furnace burners to perform heat treatment or melting. Industrial furnaces are used to provide heat of more than 400 degrees Celsius. Furnace load and operating temperature specify the type and the number of industrial burners that should be installed on the furnace.
Industrial burners are divided into premixed and nozzle mix burners based on fuel and air mixing. In premixed burners before the nozzles outlets, fuel and air mix together. In nozzle-mixed burners, fuel and air mixing occur after the nozzle exits.
A centrifugal fan supplies the combustion air. For high-temperature industrial furnaces, it is necessary to preheat the combustion air with a recuperator. The recuperator is a heat exchanger that transfers the flue gas waste heat to the combustion air.
Each type of «industrial burner» has an air damper and a fuel valve that control the inlet flow rate of air and fuel based on the furnace load. Air and gas mix and ignitor supply the combustion activation energy and the combustion chain form the flame. The burner head and its flame cover affect the flame shape.
According to furnace operations, industrial burners can install vertically or horizontally on furnaces. Furnace burners are categorized into direct or indirect flame, high-velocity, flameless, oxygen-enriched, regenerative, and recuperative.
The «furnace industry» and products determine the type of flame contact. In many heat treatment processes, where the combustion gases must not come into contact with the products, indirect flame burners are used. Radiant tubes connect to the burner, and the flame will propagate through them, so the radiation mechanism transfer heat to the products. Unlike indirect flame, combustion gases are in contact with products in direct flame burners.
A high-velocity burner is implied as a burner that the combustion gases’ velocity from its outlet port exceeds 90 m/s. For commercial products, the nominal value may lie within the 120 to 150 m/s range. The burner’s tile outlet should be configured such that combustion products entrain from the fire chamber back to the flame root to shape a uniform temperature distribution. Since the 1960s, high-velocity burners have been widely used in many industries like process applications, metallurgies, and ceramics.
Flameless, mild, or HiTAC combustion is a process in the flame that is not visible to the naked eye. As an advantage of this method, we can point out that NOx and CO emissions are extremely low because of high reactant mixing and homogeneous low flame temperature. Achieving flameless combustion can occur using oxygen dilution (MILD), combustion air preheating (HiTAC), and colourless distributed combustion (CDC) methods.
A way to increase combustion temperature is using Oxygen Enhanced Combustion (OEC). In this method, pure oxygen has injected directly into the industrial furnace burner. Oxygen-enriched burners can work with both an air-oxygen mixture and pure oxygen. In industries, these burners are known as air-oxy fuel and oxyfuel burners, respectively. It should be noted that flame temperature and NOx formation in air-oxy fuel burners arise. Unlike air-oxy fuel burners, oxyfuel NOx emission is nearly zero due to the absence of nitrogen on the reactant side.
regenerative burners have been manufactured to recycle heat from exhaust gases and reduce fuel consumption. For any preheater, a compact regenerator burner can provide nearly fully optimized performance (efficiency of about 90%) in recovering the heat from the exhaust gas. Regenerative burners are installed on opposite sides of the furnace wall. A low-cost and maintenance operation can be provided by combining a high percentage of preheating and minimum operating environment sensitivity.
One complete and compact Regenerative burner can act as double-duty equipment. It has a set comprising two burners, reversing valves, reversing logic, and two regenerators. The regenerative burner includes a ceramic ball bed that absorbs heat from exhaust gases. During a paired operation, one burner can fire with fresh air fed to its regenerator, and another can act as an exhaust port to pass the flue gas through it. The firing burner’s combustion air is preheated by removing the heat stored in the ceramic balls. The burners can change operation between firing and exhausting when the furnace product or process needs heat.
One of the integral parts of any combustion system may be energy recuperation. The heat recovery equipment is a separate component of some heat processing systems. Combustors may be referred to as either regenerative or recuperative among the methods used for heat recovery.
When combustion air preheating is required, using the sensible energy of hot combustion gases may be a good choice. This can be done using low- to medium-temperature heat exchangers (up to 700 °C) recuperators and commonly act as counterflow ones. Because of the limitations of metals, the recuperators are typically used in lower-temperature processes, and they may be made of ceramics when a higher-temperature process is needed.
A heat exchanger is built into the recuperative burner so that the hot combustion products are exhausted through it, where they can preheat either the fuel, the oxidizer, or both. Various streams’ large temperature and pressure differences may cause a challenging design. Using the heat recuperation method in the burner has many advantages, instead of an external heat exchanger to recover furnace hot gases energy. External heat exchangers need a considerable amount of vast and insulated ducts. Nevertheless, the built-in heat exchanger may be less efficient in comparison with an external one and consequently tend to have lower preheat temperatures. As mentioned above, flame radiation enhances when incoming fuel or oxidizer has preheated because of flame temperature increase.
The self-recuperative burners are a single package of burner components and a heat exchanger. They are commonly used on single-end style radiant tubes or, in some cases, newer styles of recirculating radiant tubes. There is no heat loss in the air side because of the direct installation of burner nozzles on the end of the air side of the recuperator.
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