Burners control

They include the combustion chamber, gas burners, burner controls, and exit temperature indicator. Usual exit temperatures for the destruction of most organic materials are in the range of 650°-825°C, with retention times at the elevated temperature of 0.3-0.5 sec. 

Logical control panel arrangements. Figure 4.7 is an illogical arrangement of burner controls on a kitchen stove. 

Figure 4-7. An illogical arrangement of burner controls for a kitchen stove (from Norman, 1992)- Note The author who drew this figure had a difficult time getting it "right."His instinct was to connect the controls and burners in a logical fashion.

Fire tubes, especially in heater treaters, where they can be immersed in crude oil, can become a source of ignition if the tube develops a leak, allowing crude oil to come in direct contact with the flame. Fire tubes can also be a source of ignition if the burner controls fail and the tube overheats or if the pilot is out and the burner turns on when there is a combustible mixture in the tubes. 

Fire tubes can lead to fire or explosion if there is a leak of crude oil into the tubes or failure of the burner controls. An explosion could be sudden and lead directly to injury. Therefore, a high level of safety is required. 

If the products of combustion can be diluted so that the carbon dioxide content is not greater than 1 per cent it is permissible to discharge them at ground level. This is the principle of the system shown in Figure 19.7, in which fresh air is drawn in to dilute the flue products which are discharged preferably on the same wall as the inlet to balance against wind effects. It is essential to interlock the airflow switch with the burner controls. 

The burner-control equipment for both oil and gas is to the current standard for this type of equipment. 

Release the burner controls to modulation so that the burner can be driven to high fire, according to demand. 

The amount of process plant that can be defined accurately as automatic is relatively small, and manual intervention is often involved at some stage. The relevant design criteria are therefore often IM/12 or IM/18. In practice, fully automatic burner controllers tested and certified by British Gas are available that comply with the requirements of BS 5885. Although these have features which may not be applicable to non-automatic plant, it may be more appropriate to use such a controller, particularly as its safety is well proven. It may also be less expensive than buying and installing separate timers, relays, etc. For some processes (for example, those that do not need and cannot tolerate a long purge) such controllers may not be appropriate. 

For hot water boilers the burner controls will be similar but controlled by a combination of pressure and temperature signals. A single overriding level control will be fitted to the flooded boiler to protect against any accidental low-water condition. 

This is very common nowadays to allow bargaining on fuel price or to arrange an interruptible gas tariff, which is backed up at times of peak demand with a stored oil supply. Most types of oil and gas burner are available in dual-fuel form, normally with gas burner design wrapped around the arrangement for oil firing. This is usually the more difficult fuel to burn, particularly in the case of residual heavy oils. Fuel selection is normally by a switch on the burner control panel after isolation has taken place of the non-fired fuel. To avoid the cost and complexity of the fuel preheating on oil firing, smaller systems use gas oil as the standby fuel. 

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

We used a Taylor candy thermometer for controlling the beaker bath temperature, and adjusted the gas stove burner controls as needed. From time to time, more water had to be added to the bath surrounding the beakers, due to evaporation. 

Some application areas of gas sensors are described in chapter 5.3, including gas and fuel powered domestic burner control, air quality sensing, indoor detection of CO, and natural gas detection. Several further applications of gas sensors are still in the development stage, e.g. for cooking and frying control, or for controlling the self-cleaning procedure (pyrolysis) of ovens. 

In addition there had to be created a new furnace control device. Now a burner control exists which uses the sensor s signals to adjust the gas-air ratio under various circumstances with a very low emission of polluting gases (CO and NOx). The new appliance is suitable for different gas types without any adjustments, not even at the first start after installation. 

Domestic Burner Control (Fuel Burners, Gas Condensing Boilers)... 

In household heating systems running on gas or oil the presence of the flame has to be surveyed. If the flame extinguishes, a burner control system has to reignite the flame or the fuel supply has to be stopped. Several flame-sensing mechanisms are used in the control systems. 

Thermoelectric flame failure detection Analog burner control systems Safety temperature cut-out Mechanical pressure switch Mechanic/pneumatic gas-air-ration control Thermoelectric flame supervision Thermal combustion products, discharge safety devices Electronic safety pilot Electronic burner control systems Electronic cut-out with NTC Electronic pressure sensor/transmitter Electronic gas-air-ration control with ionisation signal or 02 sensor Ionisation flame supervision Electronic combustions product discharge safety device... 

Flame safeguards Table 3.61 gives a summary of the relative features of the various flame sensors that are used in burner controls. The presence of flame can be established by measuring the (1) heat generated, (2) ability to conduct electricity (ionization), and (3) radiation at various wavelengths, such as visible, IR, and UV. 

The volatility of fuel oil must be uniform, from batch to batch, if too-frequent resetting of burner controls is to be avoided and if maximum performance and efficiency are to be maintained. Information regarding the volatility and the proportion of fuel vaporized at any one temperature may be obtained from the standard distillation procedure (ASTM D-86, IP 123). The distillation test is significant for the distillate fuels because it is essential that the fuels contain sufficient volatile components to ensure that ignition and flame stability can be accomplished easily. 

Oil applications are based on pressure atomization technology even if small power application solutions are available based on oil evaporation by heat. Electronic control of the fuel/air ratio previews an actuator to move a butterfly for controlling the air flow and an actuator to move the oil pressure regulator. For gas, two actuators control two butterflies, one for gas and one for air, even if fhe gas pneumatic valves (whose working principle is based on a pneumatic feedback) are widely used. More advanced burners control air flow changing the fan speed, reducing the pressure drop in the hydraulic pipes and valves. Despite this, a butterfly valve is often necessary to control startup operation, especially for high power applications. 

The introduction of a microprocessor in burner control introduced several new functions, starting from diagnosis to fuel consumption indication. 

The combustion burner control could be to follow several differenf physics principles, fhe most actually used are ... 

Controlling the pressure and flow of a fuel gas alone cannot dehver a constant heat flow if the gas composition varies. The control problems presented by gas composition variations can be overcome by adding a hi-speed calorimeter to monitor heat value and by using a conventional flow orifice to measure flow to an existing burner control system. These two measurements, heat value and flow rate, in combination with the conventional control and feedback loop based on loan, provide the basis for effective, continuous feed forward control of the burning process. 

Many systems, however, fail to adhere to these principles—for example, the layout of stove burner controls fails to conform to the topological consistency principle (see Figure 2). Controls located beside their respective burners (Figiure 2[h] and 2[confusions caused by arrangements shown in Figure 2(a) and 2(c). 

Figure 2 Alternative Layouts of Stove Burner Controls.

To assure minimum bottom temperature difference across the furnace width of the load, two T-sensors should be installed, one on each side of the furnace (arrows 3 and 4 in fig. 3.26). The 4 T-sensors should be positioned 1 to 3 in. (25 to 75 mm) above the pier top in the wall opposite the high-velocity burners, controlling the fuel input (with combustion air flow held constant). The 3 T-sensor should be at the same elevation as the 4 sensor, on the same side as the high-velocity burners. In a heavily loaded furnace at forging temperature, the two opposite lower sensors should be within 6°F (3.3°C) of one another. 

Butt-welding furnaces that use type E convex tile radiation burners instead of impingement are controlled by eye measurement of strip temperature. With impingement heating (type H burners), control is by observing the width of strip edge burning, a much more accurate way. 

Pasminco s Kroll-Betterton antimony debismuthising plant has been in operation for almost 20 years and the process has been well documented. The upgrade was carried out simultaneously with the batch refinery stages. Modifications to kettle size, burner control systems, and equipment used to dissolve the calcium and magnesium reagents and to remove the bismuth crusts have all enhanced the ability of the plant to run at the design rate of up to 40 t/h, and remove bismuth fi om input bullion at 0.05-0.06% down to <0.005% Bi. 

Upgrade boiler/burner controls. On larger boilers (100 hp [75 kW] plus), replace jackshaft fixed fuel-air relationship controls with distributed digital/servomotor controls and exhaust-gas analysis systems (O2, CO, CO2). With this type of control system, excess air can be precisely controlled. 

Shutdown systems for processes Interlocks for dangerous machinery Fire and gas detection Instrumentation Programmable controllers Railway signaling Boiler and burner controls Industrial machinery Avionic systems... 

Some specific design guidance is given for pressure and flow control, gas holder control, burner control, fire and gas detection and process shutdown systems. 

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