Heater outlets

In a submerged-tube FC evaporator, all heat is imparted as sensible heat, resulting in a temperature rise of the circulating hquor that reduces the overall temperature difference available for heat transfer. Temperature rise, tube proportions, tube velocity, and head requirements on the circulating pump all influence the selec tion of circulation rate. Head requirements are frequently difficult to estimate since they consist not only of the usual friction, entrance and contraction, and elevation losses when the return to the flash chamber is above the liquid level but also of increased friction losses due to flashing in the return line and vortex losses in the flash chamber. Circulation is sometimes limited by vapor in the pump suction hne. This may be drawn in as a result of inadequate vapor-liquid separation or may come from vortices near the pump suction connection to the body or may be formed in the line itself by short circuiting from heater outlet to pump inlet of liquor that has not flashed completely to equilibrium at the pressure in the vapor head. 

Cause A blind had been left in the heater outlet... 

Temperature at outlet of heater should be about 5 to 15°F above hydrate temperature. Choose temperature at heater outlet as 75°F. 

Heater outlet temperature, Coke drum pressure, psig °F 900-950 15-90... 

One definition of the point of absolute combustion is the point of maximum heater outlet temperature for a given amount of fuel, for any given furnace or heater (as illustrated in Fig. 20.3). Following this we... 

Figure 20.3 Point of absolute combustion in terms of heater outlet temperature.

One week I was switching the blowers when I forgot to shut one of the two down before starting up the third blower. I then had all three blowers running at once. Our normal heater outlet temperature target is 680°F, but while I had all three blowers on, the outlet temperature rose rapidly to 740°F. 

After cutting back on the air registers, operator A noticed that the heater outlet temperature dropped, so he raised the fuel rate to maintain the heater outlet temperature. He did not realize that this sequence of events was an indication of insufficient combustion air, because the convective-section oxygen analyzer still showed 7 percent 02, so he asked operator B to pinch back still further on the air registers. 

Automatic operation linked to process outlet temperature while on the bad side of absolute combustion is potentially hazardous because the heater outlet temperature will drop as a result of the reduced heating efficiency of the fuel. The automatic control will then call for more... 

Minimize fuel rate for a given heater outlet temperature (or steam production in a boiler), then operate at 0.5 to 1 percent higher oxygen. 

Three operating control variables in a delayed coker dictate the product quality and yields for a given feedstock. These variables are the heater outlet temperature, coke drum pressure and the ratio of recycle to fresh feed. 

Air is heated from 25°C to 150°C prior to entering a combustion furnace. The change in specific enthalpy associated with this transition is 3640 J/mol. The flow rate of air at the heater outlet is 1.25 m /min and the air pressure at this point is 122 kPa absolute. 

This requirement provides a significant cost in fuel gas to heat the water. At a 20,000-mVday refinery with a desalter outlet temperature of 100 C and a crude-oil heater outlet temperature of 315 C, each tenth of a percent of water carryover will result in 20,000 kg of water being heated 215 C to form... 

Atmospheric heater outlet temperature 5 Naphta recycle flow rate... 

The temperature difference between the heater outlet temperature and the peak vessel outlet temperature is 50°F. 

FIGURE 15.73 Fired heater outlet temperature control in the DCS. 

Effect of Location of Sorbent Injection Point. The effect of injecting sorbent at the baghouse inlet versus injecting into the flue gas duct 26 feet upstream at the air heater outlet was examined. The baghouse temperature was maintained at 400°F and cycle time was 30 minutes. Three size consists of NaHCC>3 were used 32, 69, and 180 pm. All tests were carried out at a... 

Tempunit TU-16A heater, outlet restrictor solvent mixture. hexane-MTBE temperature of the ultrasonic bath. 70°C duration of extraction. ... 

Effect of Fuel Pressure. Another major problem with a conventioned single-loop control is that if the fuel pressure drops, less fuel will flow through the control valve. Eventually, the liquid flowing through the process heater will have a lower temperature which is finally affected by the thermocouple in the heater outlet. When this happens, the recorder-controller signals the fuel valve to open wider letting more fuel into the process heater. Unfortunately, more time passes before the controller knows precisely how much to open the fuel valve for correct temperature control. 

Effect of Fuel Heat Content. Because process heaters often bum two or more fuels—natural gas, process plant off-gas, heavy fuel oil, or light fuel oil (each having a different Btu content)—a change in fuel to the fired heater can dramatically change the heat developed. Some time will elapse before the change in process fluid temperature is registered on the heater outlet thermocouple. 

Effect of Valve Position. With some heating fluids, certain valve positions upset the supply of heat to the furnace which requires time for a change in process fluid temperature to be detected by the heater outlet thermocouple. When this happens, the controller will make an effort to reposition the fuel valve to satisfy the furnace heat... 

Effect of Process Fluid Changes. Composition of the process fluid sometimes changes during normal operations which requires a change in the amount of heat to be absorbed. The controller tries to modify the amount of heat supplied to the heater, accommodating the change in process fluid. But, again, wide fluctuations will be observed in process fluid heater outlet temperatures. 

To reduce fluctuations in process heater outlet temperature, a cascade control system should be considered. 

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