{"id":106,"date":"2022-02-02T13:43:46","date_gmt":"2022-02-02T18:43:46","guid":{"rendered":"https:\/\/opentextbc.ca\/plumbing3e\/chapter\/describe-gas-burners\/"},"modified":"2022-08-16T14:14:42","modified_gmt":"2022-08-16T18:14:42","slug":"describe-gas-burners","status":"publish","type":"chapter","link":"https:\/\/opentextbc.ca\/plumbing3e\/chapter\/describe-gas-burners\/","title":{"raw":"Learning Task 1","rendered":"Learning Task 1"},"content":{"raw":"Burners are designed in different shapes and sizes to accommodate the wide variety of heat exchangers and combustion chamber requirements. It is important for you to know the special characteristics of the different burners you are likely to encounter in the gas industry.\n

Burner Terminology<\/h1>\nThe world of burners has its own language and terms. An introduction to some of these terms and their definitions will help you when they get used in context.\n

High fire<\/h2>\nHigh fire is the design maximum firing rate of a burner. It represents the maximum fuel input and heat output a burner can safely be operated at in a particular application.\n

Low fire<\/h2>\nLow fire is the minimum input of fuel that is required to keep a burner from flaming out. This is similar to an automobile: If gasoline intake were reduced while a vehicle was idling, the engine would stall.\n

Modulation<\/h2>\nBurner modulation is used to vary the gas input to vary the heat output to a process in order to match the heat load requirement and sustain the desired temperature. Modulating controls can regulate a burner between high and low fire in a continuously variable manner,\n

Turndown ratio<\/h2>\nThe turndown ratio is defined as the ratio of the maximum fuel input rate to the minimum fuel input rate for a modulating burner. It is used to help determine how low a boiler can modulate before it turns off. For example, the turndown ratio for a gas fired burners may be listed as 5:1. This means the burner can modulate as low as 20% off its full rated input.\n

Port loading<\/h2>\nThe term port loading refers to the amount of gas-air mixture passing through a burner that will create a stable flame. Burner port loading is expressed as the number of Btus per square inch of port area. The port loading can be changed by altering either the orifice size or the gas pressure (manifold pressure). For most applications using natural gas, a port loading between 25,000 Btus and 30,000 Btus per square inch of port area provides a stable flame.\n

Burner Types<\/h1>\nGas burners can be either mechanical or non-mechanical depending on how the combustion air is being supplied. Classifying burners can be very confusing because there are no standard definitions the following represent some of the more common industry accepted terms.\n

Non-Mechanical Burners<\/h2>\nNon-mechanical or \u201catmospheric burners\u201d rely on atmospheric pressure to supply the required combustion air. An atmospheric burner has a venturi that sucks primary air into the burner and mixes the air and gas before ignition (Figure 1).\n\n[caption id=\"attachment_28\" align=\"aligncenter\" width=\"400\"]\"\" Figure 1 Atmospheric burner[\/caption]\n\nThe operation and parts of atmospheric burners will be discussed in much greater detail in E-5 Learning Task 2, Describe Atmospheric Burners<\/a>.<\/em>\n

Mechanical Burners<\/h2>\nMechanical burners use a fan or blower to supply the required amount of combustion air and may also assist in venting the products of combustion.\n\nMechanical burners are categorized based on either; the location of the fan or blower in relation to the combustion chamber, or the air pressure being delivered through the burner and where the gas and air are mixed in the burner.\n\nHere are some of some of the types of mechanical burners.\n

Forced draft burner<\/h3>\nIn a forced-draft burner, combustion air is supplied by a fan or blower at sufficient pressure to overcome the resistance of the burner and the appliance. Therefore, the blower in a forced draft burner supplies the air to the burner and also forces the products of combustion through the appliance. The fan or blower is located upstream of the combustion zone as shown in Figure 2.\n\n[caption id=\"attachment_28\" align=\"aligncenter\" width=\"400\"]\"\" Figure 2 Forced draft burner[\/caption]\n

Induced draft burner<\/h3>\nThe induced-draft burner uses the mechanical draft produced by a fan located on the downstream, or chimney side, of the combustion zone as shown in Figure 3. The fan is designed to pull in the required air supply for combustion and vent the products of combustion with a positive vent pressure.\n\n[caption id=\"attachment_28\" align=\"aligncenter\" width=\"369\"]\"\" Figure 3 Induced draft burner[\/caption]\n

Balanced draft burner<\/h3>\nThe balanced-draft burner system has a combination of forced and induced draft, were one fan is located upstream, another is located downstream of the combustion chamber (Figure 4). The combustion air is forced through the burner and then pulled from the combustion chamber by an induced draft fan. This is more common with larger boilers with multiple passes where the flue gases have to travel a long distance.\n\n[caption id=\"attachment_28\" align=\"aligncenter\" width=\"400\"]\"combustion Figure 4 Balanced draft system[\/caption]\n

Fan-assisted burner<\/h3>\nA fan-assisted burner is a burner in which the combustion air is supplied by a mechanical device such as a fan or blower at sufficient pressure to overcome the resistance of the burner only.\n\nThe fan can be located upstream as is the case with a fan-assisted conversion burner (Figure 5 left), or downstream as in the fan-assisted combustion system shown on the right of Figure 5.\n\n[caption id=\"attachment_28\" align=\"aligncenter\" width=\"600\"]\"water Figure 5 Fan-assisted systems (conversion burner left, inducer fan-assisted right)[\/caption]\n\nThese systems are often described as forced or induced fan assisted systems, which can make them easy to confuse with the previously described forced and induced draft powered burners. For fan-assisted systems the fan only gives a more precise control over the air entering the combustion chamber, compared to that of a natural draft burner. The combustion products are vented naturally with a nonpositive vent stack pressure.\n

Pre-mix burners<\/h3>\nIndustrial combustion systems that require a short, hot flame with a high-heat release may use a burner that pre-mixes the gas and air upstream of the burner. There are three types of pre-mix burners:\n