Furnace automatic temperature control

If you try to operate a furnace, fired heater, or boiler with too little combustion air to starve the burners of oxygen to smother or bog down the firebox, then you will likely cause afterburn or secondary combustion in the stack, you will not be able to operate on automatic temperature control, and may even destroy the equipment altogether. 

If we have the furnace on automatic temperature control while we are not using enough combustion air, and if the control valve on the fuel gas then opens to allow more fuel to the burners in order to either maintain or perhaps increase the furnace outlet temperature, the extra fuel will not burn efficiently. In fact, the extra fuel is likely to reduce the heater or furnace outlet temperature rather than increase or maintain it, as there is already a shortage of air and it cannot bum properly and tends to cool the firebox. The automatic temperature controller... 

For large installations several hundred couples may be connected to a switchboard and the operator of the board connects the couples successively to the indicator. The switchboard is frequently designed somewhat similar to an ordinary telephone distributing board. Often in these large installations communication between the operator of the switchboard and the operator of the furnace is maintained by a system of colored electric lamps. This method of semi-automatic temperature control is meeting with great success in the industries. 

Catalytic activity data were obtained by using a conventional fixed-bed reactor at atmospheric pressure. A stainless steel tube with an inner diameter of 12 mm was chosen as the reactor tube. Catalyst (3.5 cm, ca. 1.8 g) was placed on ceramic wall at the lower part of the reactor. The upper part of the catalyst bed was packed with 10 cm of inactive ceramic spheres (2 mm O.D.) to preheat the gas feed. The furnace temperature was controlled with a maximum variation of 2°C by an automatic temperature controller. The gas exiting the reactor was led to a condenser to remove water vapour. The remaining components were continuously analysed by non dispersive infrared (CO and CO2), flame ionisation (HC), magnetic susceptibility (O2), and chemiluminiscence (NOx). 

Caution. A reliable automatic temperature controller should always be used on the lower temperature furnace to avoid dangerous I2 pressures. 

With a fan-furnace heating system, once the temperature is reached, the fan is controlled to start automatically. Should fan failure occur, provision should be made to damp down the furnace automatically to avoid overheating s causing tube damage. 

Temperature controller — A device that measures the temperature and automatically controls the heat input into the furnace. 

A malfunctioning high-temperature furnace trip caused a major tray upset in a large ethylbenzene fractionator. Figure 17-3 shows the tower control system. When the circulation pump briefly failed, the flow of hot vapor to the tower was interrupted. The tower temperature controller was called for more heat, and furnace fuel firing consequently increased. At this point, the automatic furnace shutdown system should have tripped off the furnace fuel due to the excessive furnace outlet temperature. This trip failed to function. 

Control Devices. Control devices have advanced from manual control to sophisticated computet-assisted operation. Radiation pyrometers in conjunction with thermocouples monitor furnace temperatures at several locations (see Temperature measurement). Batch tilting is usually automatically controlled. Combustion air and fuel are metered and controlled for optimum efficiency. For regeneration-type units, furnace reversal also operates on a timed program. Data acquisition and digital display of operating parameters are part of a supervisory control system. The grouping of display information at the control center is typical of modem furnaces. 

A special film holder allows transportation of the film with various rates. Time marks are printed automatically on the film for correlating the X-ray patterns to specific times and temperatures in the TMBA curves. The temperature program of the X-ray camera furnace is regulated by the thermobalance heating control system. Up to the maximum temperature of 1200 °C usual heating rates can be varied from 0.2 to 4 °C/min. The temperature of the impact plates can be held constant between room temperature and 450 °C and is recorded during the... 

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