Burners capacity

Burner Capacity - The maximum heat output (in Btu per hour) released by a burner with a stable flame and satisfactory combustion. 

The most common furnace size is 3.5 m diameter by 5 m long with an effective woiking volume of 7 m. Maximum rotational speed is 1 rev/min. Burner capacity is of the order of 2.5 MW and furnace gas volume 10 000 Nm /h. This volume may double with afterburning and dilution prior to gas cleaning. Ventilation air covering the furnace surrounds and ancillary operations can total up to 50 000 NmVh for such a furnace installation. 

The rate of heat release is the measure of burner capacity. If the fuel gas control valve to the heater is wide open, the burner capacity limits furnace duty. Gas burners can easily be expanded by enlarging the holes in the burner tip. Alternately, piping changes will sometimes increase the gas pressure to the burners. 

The pilot gas can be a separate connection or can be connected downstream of the main gas line, depending on the burner capacity. Generally, a single shutdown valve on the pilot gas line is adequate. A pressure regulating valve is also required on the pilot gas line and is generally installed downstream of the shutdown valve. This maintains certain downstream pressure, and no attempts are made to control reboiler temperature while the system is on pilot operation. 

The start gas connection is taken from the main gas line and is taken from between two main gas shutdown valves. Depending on the burner capacity, different arrangements are possible, and these are discussed in the following text ... 

Burner capacity not exceeding 500 MJ/h The configuration is shown in Figure 5.12A. In this arrangement, no isolation valve is provided on the start gas connection. 

Burner capacity exceeds 500 MJ/h but is less than 5 GJ/h The configu-rahon is shown in Figure 5.12B. This configuration is similar to the previous one with a shutdown valve on the start gas line. 

Burner capacity exceeds 20 GJ/h The configuration is shown in Figure 5.12D. For this configuration, all shutdown valves are to be installed with proof-of-closure switch. 

Commercially, the burner chamber and the absorber cooler sections are combined as a single unit for small-scale production. However, in large capacity plants, these units are separated. A typical commercial unit is schematically described in Figure 5 (32). 

Many kilns that formerly were direct coal-fired or producer-gas verticals were retrofitted to natural gas firing with center-burners and after World War II, dramatically improving lime quaUty, kiln capacity, and fuel efficiency. By the 1960s, this improved vertical kiln had lost favor to rotary and other special kilns because of the supply and cost problems of oil and gas in the United States and the spectacular improvement in rotary kiln performance. Many natural gas-fired center burners were permanently closed and dismanded because they could not be converted to coal. However, the reverse occurred in Europe where the extensive oil and gas discoveries heightened interest in the new, advanced vertical kilns. 

Pan and cascade burners are generally more limited ia flexibiHty and are useful only where low sulfur dioxide concentrations are desired. Gases from sulfur burners also contain small amounts of sulfur trioxide, hence the moisture content of the air used can be important ia achieving a corrosion-free operation. Continuous operation at temperatures above the condensation poiat of the product gases is advisable where exposure to steel (qv) surfaces is iavolved. Pressure atomiziag-spray burners, which are particularly suitable when high capacities are needed, are offered by the designers of sulfuric acid plants. 

Other burners are used for low capacity operations. A cascade or checker burner, ia which molten sulfur flows down through brick checkerwork countercurrent to a flow of air, is used ia small units with a sulfur trioxide converter to condition gases entering electrostatic precipitators at boiler plants operating on low sulfur coal. A small pan burner, which is fed with soHd, low carbon sulfur, is used to produce sulfur dioxide for solution ia irrigation water to control the pH and maintain porosity ia the soil. The same type of burner is used to disiafect wastewater ia this case sulfur dioxide is used iastead of chlorine. 

Cracking reactions are endothermic, 1.6—2.8 MJ/kg (700—1200 BTU/lb) of hydrocarbon converted, with heat supplied by firing fuel gas and/or fuel oil in side-wall or floor burners. Side-wall burners usually give uniform heat distribution, but the capacity of each burner is limited (0.1—1 MW) and hence 40 to 200 burners are required in a single furnace. With modem floor burners, also called hearth burners, uniform heat flux distribution can be obtained for coils as high as 10 m, and these are extensively used in newer designs. The capacity of these burners vary considerably (1—10 MW), and hence only a few burners are required. The selection of burners depends on the type of fuel (gas and/or liquid), source of combustion air (ambient, preheated, or gas turbine exhaust), and required NO levels. 

The circular burner shown in Fig. 27-17 is widely used in horizontally fired furnaces and is capable of firing coal, oil, or gas in capacities as tigh as 174 GJ/h (1.65 X 10 Btii/h). In such burners the air is often swirled to create a zone of reverse flow immediately downstream of the burner centerline, which provides for combustion stability. 

A butterfly valve in the line to the first stage seal drum limits the maximum flow to the first stage burner. The valve is set by observing the burners while flaring at design capacity. Once adjusted, the valve should be locked in position. 

Most electricity from biofuels is generated by direct combustion. Wood fuels are burned in stoker boilers, and mill waste lignin is combusted in special burners. Plants are generally small, being less than 50 MW in capacity. There is considerable interest in combustion of biomass in a process called cofiring, when biomass is added to traditional fuels for electricity production. Cofiring is usually done by adding biomass to coal, but biomass also can be cofired with... 

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