Preheater burner

Oil preheaters, burners, stokers, primary and secondary air ports, and burner control linkages should be inspected for fouling or wear. 

A recent development is the Uhde [532] three-stream burner with an adjustable tip. A portion of the of oxygen enters through the center nozzle, the remainder through the outer annulus, the oil is fed through the inner annulus. The center oxygen nozzle also accommodates the preheat burner. This combi-burner concept avoids the change from preheat burner to process burner in the start-up phase, a cumbersome procedure necessary when using the traditional two-stream Texaco burner. As tested in a demonstration plant the carbon conversion could be increased to better than 99.6%, which means a reduction soot formation by a factor better than 5. 

The VUB pilot plant consists of a feeding system (a hopper equipped with a rotary valve and a conveyor screw), the fluidized bed reactor, preheating burner, cyclone and a control system. The bubbling fluidized bed gasifier has a capacity of 400 kg/h and consists of a bed (0.8 m diameter/0.6 m height) with an extended freeboard section (1.2 m diameter/2 m height). More technical details about the gasifier can be found in [16]. 

Preheat burners are usually designed to increase the temperature of the contaminated gases to the required catalyst discharge gas temperature without regard to the heating value of the contaminants (especially if considerable concentration variation occurs). 

The reviews by Spivey [3] and by Jennings et al. [156] are excellent sources for further details on catalytic incineration of volatile organics emissions. Spivey [3] describes two types of techniques for removal of VOC from off-gases, namely one without preheater and one with a direct flame preheater. From an economically point of view it is more beneficial to carry out the catalytic oxidation at lower temperatures. In a catalytic incinerator, sometimes called an afterburner, VOCs are oxidized into carbon dioxide and water. The efficiency is about 70-90%. The incinerator has a preheat burner, a mixing chamber, a catalyst bed, and a heat recovery equipment. Temperatures of about 590 K are sirfficient for the destruction of VOCs. Various catalyst geometries have been used metal ribbons, spherical pellets, ceramic rods, ceramic honeycombs, and metal honeycombs. Precious metals such as platinum and palladium are often used in catalytic incinerators. 

Combustion air blower inlet preheat Burners are mounted upstream of a blower inlet to protect against thermal shock caused by ambient air in extremely cold climates (-40°F/°C and below). This arrangement is only suitable when the air will be used in a combustion process as it will contain combustion products from fhe duct burner. 

Heat input to the roaster is necessary during start-up and is achieved by three removable preheat burners. Once a bed temperature of about 700°C is achieved, oxidation of the sulphide feed slurry provides adequate heat to maintain temperature. 

Noncatalytic Approaches. Three system design approaches have been proposed and studied in combination with catalysts to reduce the cold start emissions. The preheat burner uses the gasoline fuel in a small burner placed in front of the catalyst. The burner is turned on during cold start and the heat generated warms up the catalyst so that the catalyst is already hot when the cold exhaust from the manifold reaches it (76). 

Controlled heating of the refractory by means of a preheat burner (duration 36 hours)... 

The heavy fuel should be heated systematically before use to improve its operation and atomization in the burner. The change in kinematic viscosity with temperature is indispensable information for calculating pressure drop and setting tbe preheating temperature. Table 5.20 gives examples of viscosity required for burners as a function of their technical design. 

Pulverized lime or limestone injected into flue gas (often through burner). SO2 absorbed on soHd particles. High excess alkah required for fairly low SO2 absorption. Finer grindings lime preheat, flue gas humidification benefit removal. Particulate collected in baghouse. 

Chemistty of Partial Oxidation. The process is carried out by injecting preheated hydrocarbon, preheated oxygen, and steam through a specially designed burner into a closed combustion vessel, where partial oxidation occurs at 1250—1500°C, using substoichiometric oxygen for complete combustion. 

Burners and combustion air ports are located in the walls of the furnace to introduce either heat or air where needed. The air path is countercurrent to the sohds, flowing up from the bottom and across each hearth. The top hearth operates at 310—540°C and dries the feed material. The middle hearths, at 760—980°C, provide the combustion of the waste, whereas the bottom hearth cools the ash and preheats the air. If the gas leaving the top hearth is odorous or detrimental to the environment, afterburning is required. The moving parts in such a system are exposed to high temperatures. The hoUow central shaft is cooled by passing combustion air through it. 

Regulations require that the incinerator furnace be at normal operating conditions, including furnace temperature, before hazardous wastes are injected. This requires auxiUary fuel burners for furnace preheating. In addition, the burners provide heat when the wastes burned are of low heating value. Auxihary burners are sized for conditions where Hquid wastes are injected without the addition of high heating value wastes. 

Because large amounts of water vapor are produced by combustion of H2S or spent acids, ambient, not dried, air is suppHed to the burners. In some cases, burners are operated at pressures slightly below atmospheric to pull in outside air in other cases, preheated combustion air at low pressure may be suppHed by ducts. 

The success of preheater kiln systems led to precalciaer kiln systems. These units utilize a second burner to carry out calciaation ia a separate vessel attached to the preheater. The flash furnace (57), eg, utilizes preheated combustion air drawn from the clinker cooler and kiln exit gases and is equipped with an oil burner that bums about 60% of the total kiln fuel. The raw material is calciaed almost 95%, and the gases continue their upward movement through successive preheater stages ia the same manner as ia an ordinary preheater. 

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. 

Instead of gas turbine exhaust, air preheat has been used in some plants to reduce fuel consumption. Flue gas leaving the furnace stack passes through an air preheater, and the preheated air is suppHed to the burners. By using mostly hearth burners, the duct work and the investment cost can be minimised with air preheat and gas turbine exhaust. It is also possible with 100% waH-fired furnaces, and has been proven in commercial operation (34). 

CTF 50 and 400 indicate approximate preheat temperature, F, for atomization of fuel in burners (terminology used in British Standard B.S. 1469). Properties depend on distillation range, as shown, and to a lesser extent on coal source. 

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