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Chapter 10
FIRED HEATERS (FURNACES)
OBJECTIVES
After studying this chapter, the student will be able to:
▪ Describe the various types of direct-fired heaters.
▪ Explain the operation of an indirect fired heater.
CHAPTER 10 REVIEW QUESTIONS
1. What are carbon deposits in the tubes of a furnace called? Answer: Coke deposits.
2. Describe flameout. Answer: Flameout occurs in a furnace when the burner flame goes out
3. What is a hot spot? Answer: A hotspot occurs in a fired heater when a furnace tube,
4. What section of the furnace has the highest temperature? Answer: The firebox in the
5. Where are the convection tubes located in a furnace? Answer: The convection tubes are
6. Where are the radiant tubes located in a furnace? Answer: Radiant tubes are located in or
7. Describe flame impingement. Answer: Fired heater burner flames can be from three feet
8. Air enters the furnace in five ways. Name them. Answer:
a. primary air
b. secondary air
9. List the basic components of a furnace. Answer:
Fired heaters come in a variety of shapes and sizes. They have different tube
arrangements and feed inlets; they burn different types of fuels and have different burner
designs. Furnaces have certain things in common.
a. Fire box
b. Radiant tubes
10. What is the shockbank? Fired heater tubes located directly above the firebox. Answer:
11. What is the "charge" of a furnace? Answer: The initial flow into the fired heater is
12. Describe the bridgewall section in a furnace. Answer: The bridgewall is a section of
13. Describe a natural-draft furnace. Answer: Natural draft furnaces are not equipped with
14. Describe how forced, induced, and balanced-draft furnaces operate. Answer: When fans
15. Define spalled refractory. Answer: Spalled refractory—an aging refractory that has
cracked or deteriorated over time; a refractory that has not cured or dried properly; or a
16. Explain the importance of proper draft control in a furnace. Answer: Draft—negative
pressure of air and gas at different elevations in a furnace. Controlling excess oxygen in
17. Describe what is meant by sagging or bulged tubes. Answer: Sagging or Bulged tubes—
occur when guides or supports break, inside of tube fouls, flame impingement, reduced
18. The floor of the furnace is covered with what type of material? Answer: The floor of the
process heater has a 6 in. layer of heat-resistant castable, capped with high-temperature
19. Describe the return bend designs in the convection section. Answer: The convection
20. Excess airflow in the furnace will have what effect? Answer: Excess airflow will
decrease furnace temperatures around the burners and force the automatic controls to
increase natural gas flow rates to the burner, wasting money. As hot combustion gases
rise, cooler air is entrained causing the temperature to decrease. Excess air enhances this
