Furnace pressure

For given combustion air, waste, and auxiUary fuel feed rates to the incinerator, furnace residence time decreases as furnace pressure decreases. 

Velocity flame stoppers have been used for feeding waste fuel gas to furnace burners when the gas can become flammable due to contamination with air. They have also been used for feeding waste or depleted air streams to furnaces when the air streams can become contaminated with flammable gases (Howard 1982). It should be noted that a furnace pressure transient may render this device ineffective and consideration should be given to providing an upstream detonation flame arrester. In this arrangement a demand will only be placed on the detonation flame arrester when the velocity flame stopper fails. Therefore, detonation flame arrester maintenance should be minimal. 

Fire tube boilers usually do not have ID fans because they normally can obtain sufficient ID from the stack s natural draft. However, they do employ FD fans, which provide a positive furnace pressure. 

Large WT boilers generally have a balanced draft system (i.e., a combination of both FD and ID fans) and usually operate at negative furnace pressure (-0.1 to -0.5 inch of water) to provide for better control of both the furnace flue-gas pressure and the fuel-air combustion process. 

Checks to the air and flue gas system include visually inspecting the furnace and periodically monitoring all fans, levels of draft, furnace pressure, excess air demands, and combustion efficiency. 

A system of balancing induced draft and forced draft to a large WT boiler controlled primarily by dampers. In fact, large WT boilers tend to be specifically designed to operate at a slightly negative furnace pressure. 

Pyrrole, alkyl pyrroles, benzeneacetonitrile and benzenepropanenitrile. Pyrolyser continuous mode micro furnace pyrolysing injection system Pyrojector (SGE, Austin, Texas, USA) furnace pressure 14 psi purge flow 0.5 ml min 1 [28],... 

Figure 11.2 Py/silylation GC/MS chromatograms of aged linseed oil pyrolysed in the pre sence of HMDS, (a) Pyrogram obtained with a microfurnace pyrolyser pyrolysis temperature 600 °C furnace pressure 14 psi purge flow 0.5 ml min (b) Pyrogram obtained with a resistively heated filament pyrolyser pyrolyser interface I80°C transfer line 300°C valve oven 290°C. 1, Hexenoic acid, trimethylsilyl ester 2, hexanoic acid, trimethylsilyl ester 3, heptenoic acid, trimethylsilyl ester 4, heptanoic acid, trimethylsilyl ester 5, octenoic acid, trimethylsilyl ester 6, octanoic acid, trimethylsilyl ester 7, nonenoic acid, trimethylsilyl ester 8, nonanoic acid, trimethylsilyl ester 9, decanoic acid, trimethylsilyl ester 10, lauric acid, trimethylsilyl ester 11, suberic acid, trimethylsilyl diester 12, azelaic acid, trimethylsilyl diester 13, myristic acid, trimethylsilyl ester 14, sebacic acid, trimethylsilyl diester 15, palmitic acid, trimethylsilyl ester 16, stearic acid, trimethylsilyl ester...

To make sense of the draft measurements so that we can use them to evaluate furnace pressure drop, proceed as follows ... 

Crushed coal Cyclone furnace—pressure or suction 10-15... 

Combustion calculations show that an oil-fired watertube boiler requires 200,000 lb/h (25.2 kg/s) for air of combustion at maximum load. Select forced- and induced-draft fans for this boiler if the average temperature of the inlet air is 75°F (297 K) and the average temperature of the combustion gas leaving the air heater is 350°F (450 K) with an ambient barometric pressure of 29.9 inHg. Pressure losses on the air-inlet side are, in inFLO air heater, 1.5 air supply ducts, 0.75 boiler windbox, 1.75 burners, 1.25. Draft losses in the boiler and related equipment are, in inH20 furnace pressure, 0.20 boiler, 3.0 superheater, 1.0 economizer, 1.50 air heater, 2.00 uptake ducts and dampers, 1.25. Determine the fan discharge pressure and horsepower input. The boiler burns 18,000 lb/h (2.27 kg/s) of oil at full load. 

It is also recommended that the experimenter thoroughly analyze what is being collected to ensure the necessary data will be available for the analysis that will be done. For example, if the thermal efficiency of a combustion process will be calculated, the experimenter needs to measure both the composition and the temperature of the exhaust products, among other variables such as the fuel flow rate and composition, the combustion air flow rate, the furnace pressure, and the furnace skin temperature. If the actual water content in the exhaust products is not measured, which is often the case, it can be calculated knowing the other components in the stream and the fuel composifion and flow rate. The furnace air leakage can be calculated based on the flue gas composition and combustion air flow rate. The point is that the experimenter should carefully check... 

In addition, video cameras are positioned on the furnace side, and above the furnace horizontal exhaust section. Image processing is performed on raw video camera data to analyze and quantify flame shape and luminosity. Finally, an electric damper in the chinmey duct controls the furnace pressure to simulate various air-in leakage conditions. 

Fig. 1.18 Car-hearth heat treat furnace with piers for better exposure of bottom side of loads. The spaces between the piers can be used for enhanced heating with small high-velocity burners. (See chap. 7.) Automatic furnace pressure control allows roof flues without nonuniformity problems and without high fuel cost.

Figure 3.5 shows a 40 ft (12.2 m) long car-hearth in a 17.5 ft (5.3 m) high fiber-lined furnace with high-velocity burners at top and between the piers. Automatic furnace pressure control makes it possible to use top flues. Drilled square air manifolds shoot curtains of air across the flue exits as throttleable air curtain dampers for furnace pressure control. 

Bottom flueing is preferred, but in-the-wall vertical flues have been found too costly, and they pull a harmful negative pressure at the hearth level. With top firing, the best arrangement is hearth-level flues with automatic furnace pressure (damper) control. If fired with top and bottom burners, use of a roof flue with automatic furnace pressure control is suggested. The flue location should be determined to enhance the design circulation pattern. (See chap. 7.)... 

Use an automatic furnace pressure control with the setpoint at -t-0.02" wc (0.05 mm water gauge) to prevent air inflow... 

Al. Lower first investment cost. Less maintenance, because fewer moving parts. Save fuel if need is intermittent. Save fuel if new loads cannot be put in place promptly. Sometimes more versatile as to product size, shape, and temperature cycle. Easier to hold tight furnace pressure. Easier to hold a prepared atmosphere. 

When estimating the furnace temperature, the previous ideas must be used to properly design a furnace and estimate its fuel rale. Predicting the fuel rate if operating with delays is very questionable because the quantities of air infiltration with loss of furnace pressure can vary widely. Engineers must remember that the furnace heating capacity is determined by the actual furnace temperature, and not by the installed firing rate. 

With these two baffles, furnace pressure can be controlled, and practically all the hot combustion gases from the last zone would be forced to move to the first zone via all the other zones in the circle. In so doing, these gases would be forced to transfer more heat to the loads. 

Install a minimum of two fixed baffles and one movable baffle. Provide a furnace pressure control system if the present control is inadequate. 

With moving hearths, there must be clearance (slot) between the movable and stationary parts. Water and sand seals have been used to control hot gas loss out and cold air loss in through such slots. The term seal implies complete stoppage of gas flow in or out of the furnace. Coauthor Shannon has worked with rotary furnaces in which seals held the leakage to near zero with a positive furnace pressure of 0.1" of water (2.54 mm), but that is rarely the case. To estimate the heat loss, multiply the slot area by the radiation per unit area at the zone temperature. 

Better furnace pressure control to minimize leaks and nonuniformities... 

Sensible heat carried out of the furnace by the furnace gases (poc) is often the largest loss from high-temperature furnaces and kilns. It is evaluated by the available heat charts mentioned in section 5.1 100% — %available heat = %heat carried out through the flue. It can be reduced by careful air/fuel ratio control, use of oxy-fuel firing, and good furnace pressure control. 

Furnace Pressure Control. This type of control prevents excessive outleakage of unburned air, unburned fuel, poc, and pic (products of incomplete combustion) before they have had time to transfer heat to the loads. Chapter 7 of reference 51 describes how a variety of furnace pressure control systems work and how to evaluate the savings from their use. Furnace pressure control also prevents unnecessary infiltration (inleakage) of unwanted tramp air, which is excessive excess air. 

Note. All losses are much greater with negative furnace pressure. (1) = least loss (4) = worst loss. 

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