Question 1

In blast furnace–hot-blast practice, what medium do the blast furnace stoves heat and deliver to the furnace to enable efficient ironmaking? Specify the intended heating target (not the fuel or the off-gas).

Accepted Answer

Introduction / Context: Blast furnace stoves (often called Cowper stoves) are classic regenerator units used in ironmaking. They cyclically store heat in checker bricks and then release that heat to a flowing stream. Understanding exactly which stream they heat is essential for furnace technology: it determines combustion needs, stove sizing, and overall blast furnace efficiency. Given Data / Assumptions: The ironmaking blast furnace requires a pressurized hot blast for tuyeres. Stoves operate in alternating “on-gas” (heating bricks) and “on-blast” (heating air) modes. The goal is to raise the temperature of the oxidant entering the furnace, thereby improving thermal efficiency and reducing coke rate. Concept / Approach: In “on-gas” mode, fuel gas is burned and flue gases heat the checkerwork. After sufficient heating, flows are reversed to “on-blast” mode, where cold air passes through the hot checker bricks and emerges as hot blast. This hot air (not steam, not blast furnace gas) feeds the tuyeres to combust injected fuels/coke at the raceway, elevating flame temperatures and improving meltdown and reduction kinetics. Step-by-Step Solution: Identify the end-use stream that must be hot at the tuyeres: combustion air (the “blast”).Recognize that stoves are regenerator heat exchangers transferring stored heat to this air.Conclude that the stoves are designed to heat air, typically to several hundred degrees Celsius (often above 900°C in large plants). Verification / Alternative check: Operational descriptions of Cowper stoves uniformly state that they preheat the blast air. Process flow diagrams show air compressors/blowers feeding stoves and then the hot blast main to the tuyeres. Why Other Options Are Wrong: Blast furnace gas: Used as a fuel for the stove in “on-gas” phase, but the product stream heated for the furnace is air.Steam: Not generated by stoves; steam systems are separate utilities.None of these: Incorrect because “air” is correct. Common Pitfalls: Confusing the stove fuel (often blast furnace gas) with the stream being heated for the furnace. Assuming any hot gas leaving the stove is the same as the blast—only the “on-blast” stream is the hot air product. Final Answer: air

Question 2

In combustion engineering, oxygen enrichment of the combustion air changes several performance indicators. Which of the following does not increase when the oxygen content of air is enriched under otherwise comparable firing conditions?

Accepted Answer

Introduction / Context: Oxygen enrichment means supplying air with a higher percentage of O2 than ambient air. It is widely used to intensify combustion, raise flame temperatures, and boost heat transfer. However, not all performance metrics increase. This question probes your ability to predict directional effects on flame temperature, heat transfer, flue-gas composition, and stack losses. Given Data / Assumptions: Comparisons are made at similar firing rates and furnace conditions, except for increased O2 in the oxidant. Enrichment reduces accompanying nitrogen, thus reducing total flue-gas flow for a given fuel input. Excess O2 (residual oxygen) control remains reasonable and safe. Concept / Approach: Increasing O2 concentration in the oxidant enhances adiabatic flame temperature because less inert N2 dilutes the flame. Higher flame temperature typically increases radiative and convective heat transfer to the load (higher temperature difference and emissive power). Flue gas often shows a higher measured O2 percentage unless excess O2 setpoints are actively lowered; at constant excess, the concentration reading can be higher because of reduced N2 dilution. Stack loss primarily depends on the mass and temperature of exhaust gases. Because enrichment reduces N2, the mass of flue gas for a given heat input usually drops—tending to reduce, not increase, stack losses for comparable stack temperature. Step-by-Step Solution: Note enrichment effect: less N2, hotter flames.Infer greater heat transfer rate (hotter gases, more radiation).Recognize flue-gas O2 reading can rise unless excess trim compensates.Evaluate stack loss = m_dot(exhaust) * cp * (T_stack - T_ref); m_dot falls with less N2, so stack loss does not increase. Verification / Alternative check: Plant trials commonly report fuel savings and lower stack losses after enrichment due to reduced flue-gas mass flow, provided draft and temperature are held similar. Why Other Options Are Wrong: Flame temperature: Increases because of less inert dilution.Oxygen in flue gas: Often increases at constant excess-air control points.Heat transfer rate: Increases via higher radiative heat flux. Common Pitfalls: Assuming higher O2 always raises every metric; stack loss depends on mass flow and temperature. Confusing O2 enrichment with “more excess air,” which can have opposite effects. Final Answer: stack loss.

Question 3

In furnace performance terminology, the “rate of heat release” (a measure of heat intensity) is defined with which dimensional form for a combustion chamber?

Accepted Answer

Introduction / Context: Furnace sizing and comparison require normalized performance measures. “Rate of heat release” or “heat intensity” expresses how much heat is released per unit time per unit combustion-space volume. This allows engineers to compare different furnaces independent of their absolute size. Given Data / Assumptions: Combustion occurs in a finite chamber (combustion space). Heat input is typically based on lower or higher heating value of fuel and firing rate. We want a volumetric intensity measure to compare designs. Concept / Approach: By definition, heat intensity = (total heat released per hour) / (combustion chamber volume). In consistent engineering units, a common expression is kcal/hr/m^3 of combustion space (or kW/m^3 in SI). Using only kcal/m^3 ignores the time basis; using only kcal/hr ignores the volume basis. Hence the combined unit properly normalizes both dimensions. Step-by-Step Solution: Identify numerator: heat release rate, units of energy per time (e.g., kcal/hr).Identify denominator: combustion space volume (m^3).Form ratio: kcal/hr/m^3, the standard intensity unit. Verification / Alternative check: Textbook furnace comparisons quote limits of acceptable heat intensity in kcal/hr/m^3 to avoid unstable flames, excessive NOx, or refractory damage, confirming the unit requirement includes both time and volume. Why Other Options Are Wrong: kcal/m^3: Missing the time basis; not a rate.kcal/hr: Missing the volume normalization; cannot compare chamber intensities.None of these: Incorrect because kcal/hr/m^3 is correct. Common Pitfalls: Confusing heat flux (per area) with volumetric heat release (per chamber volume). Reporting fuel input as a rate but failing to normalize by chamber size. Final Answer: kcal/hr/m3 combustion space.

Question 4

Preheating the combustion air offers several advantages in furnace operation. Identify the item below that is not an advantage of air preheating.

Accepted Answer

Introduction / Context: Air preheaters recover sensible heat from flue gases to elevate incoming combustion air temperature. This technique is central to furnace energy efficiency and productivity. However, some properties—like the intrinsic calorific value of the fuel—are fuel-dependent and do not change with air preheat. Given Data / Assumptions: Fuel composition remains unchanged. Combustion air is heated via recuperation or regeneration. Operating goal is higher furnace efficiency and product quality. Concept / Approach: Preheated air reduces the sensible energy the flame must supply to raise oxidant temperature, effectively increasing adiabatic flame temperature and accelerating heat transfer to the load. As a result, fuel consumption typically drops for the same duty, and improved temperature control may reduce scaling of steels by limiting over-firing and shortening exposure times. But the chemical energy per unit mass or volume of fuel (its calorific value) is not altered by preheating the oxidant; it is defined by the fuel’s composition and heating value testing. Step-by-Step Solution: List common benefits: higher flame temperature, better heat flux, fuel saving, quality improvements.Identify the distractor: “increase in calorific value of the fuel.”Conclude it is not an advantage attributable to preheating air. Verification / Alternative check: Energy audits consistently report reduced specific fuel consumption with air preheating. Fuel heating value certificates remain unchanged regardless of oxidant temperature, confirming that calorific value is independent of air preheat. Why Other Options Are Wrong: Increase in flame temperature: True; less energy is spent heating the oxidant from ambient.Reduction in scale losses: Often observed due to better temperature control and shorter cycles.Saving in fuel consumption: Direct outcome of heat recovery. Common Pitfalls: Equating higher flame temperature with higher fuel heating value. Ignoring dew-point and corrosion limits when pushing air-preheat too high. Final Answer: Increase in calorific value of the fuel.

Question 5

Fuel economy in industrial furnaces can be achieved by multiple measures. Which option correctly groups common, practical methods that simultaneously help lower fuel use?

Accepted Answer

Introduction / Context: Furnace efficiency is improved by both combustion-side enhancements and enclosure/operation improvements. A holistic approach typically yields the best savings. This question validates understanding of three widely adopted strategies and whether they complement each other to reduce fuel consumption. Given Data / Assumptions: Standard fuel-fired furnace with stack, burners, and access doors. Opportunities include oxygen enrichment, air preheating, and minimizing openings/air leakage. Safety and material limits are respected. Concept / Approach: Oxygen enrichment raises flame temperature and can reduce flue-gas mass (less N2), improving heat transfer and lowering stack loss. Air preheating recovers waste heat, reducing fuel needed to reach setpoint temperatures. Sealing doors and controlling openings reduces cold air infiltration and uncontrolled heat escape—both of which otherwise raise fuel use. Together, these measures target different loss mechanisms and are additive when applied correctly. Step-by-Step Solution: Identify each measure’s effect: hotter flames, recovered heat, reduced infiltration.Recognize synergy: less fuel per ton processed and improved throughput.Choose the combined option that includes all three. Verification / Alternative check: Industrial energy assessments rank air preheaters, controlled excess O2/enrichment, and better sealing as high-impact items. Case studies show measurable drops in specific fuel consumption after implementation. Why Other Options Are Wrong: Picking only one measure ignores other proven levers and leads to suboptimal savings. Common Pitfalls: Over-enrichment without proper control can increase NOx or refractory stress. Excessive preheat risks acid dew-point corrosion in air preheaters if not managed. Final Answer: all (a), (b) and (c).

Question 6

Identify the unit that is not a recuperative furnace (i.e., it does not primarily rely on a continuous recuperator for air-preheating heat recovery).

Accepted Answer

Introduction / Context: Heat recovery devices are broadly of two types: regenerators (cyclic storage and release of heat) and recuperators (continuous heat exchange across a wall). Many furnaces can be classed by which they use, and the terminology often appears in exam questions. Here we must identify which listed unit is not principally recuperative. Given Data / Assumptions: Soaking pits and reheating furnaces commonly use recuperators or recuperative burners. Steam boilers are not classed as “recuperative furnaces” per se; they are steam generators but may have economizers/air preheaters as heat exchangers. Coke ovens (by-product type) employ classic regenerators with checker-brick chambers and periodic reversal. Concept / Approach: A recuperator transfers heat continuously from hot flue gas to cold air through a wall. A regenerator alternates the flow, storing heat in solids and then giving it back. By-product coke ovens have regenerator chambers integral to their design; therefore, they are not “recuperative furnaces.” Soaking pits and reheating furnaces frequently feature recuperation (or recuperative burners) for continuous preheating. Step-by-Step Solution: Classify each item by typical heat-recovery method.Coke oven → regenerative; soaking pit and reheating furnace → often recuperative.Select the unit that is not recuperative: coke oven. Verification / Alternative check: Process descriptions of by-product coke ovens highlight periodic flow reversal through checkerwork, the hallmark of regeneration, not recuperation. Why Other Options Are Wrong: Soaking pit / Reheating furnace: Commonly paired with recuperators for air preheat.Steam boiler: While not a “furnace type,” this option does not better fit the “not recuperative” label than the clearly regenerative coke oven. Common Pitfalls: Confusing boilers with furnaces; the question targets furnace heat-recovery classification. Assuming all high-temperature units use the same recovery method. Final Answer: Coke oven.

Question 7

Considering temperature capability, fuel-fired furnaces are generally limited to about 1700°C. Up to what approximate temperature can electric furnaces be used in industrial practice?

Accepted Answer

Introduction / Context: Electric furnaces (arc, induction, resistance) can achieve much higher temperatures than most conventional fuel-fired furnaces, because they do not depend on combustion equilibria with diluent nitrogen. Knowing the typical upper range is important for material selection and process feasibility. Given Data / Assumptions: Fuel-fired furnaces are practically constrained to about 1700°C by combustion limits and refractory service. Electric furnaces can concentrate energy directly into the charge or via resistive heating elements. Practical, widely cited upper range in industry is about 3000°C (especially for specialized arc furnaces). Concept / Approach: While laboratory plasma systems may momentarily exceed these temperatures, standard industrial electric furnaces capable of sustained operation and reasonable refractory life typically top out near 3000°C. This range enables melting of refractory metals, calcination of specialty ceramics, and high-temperature treatments that combustion systems cannot reach economically. Step-by-Step Solution: Contrast combustion vs. electrical heating mechanisms.Recognize industrially achievable, sustained temperatures.Select 3000°C as the representative upper bound. Verification / Alternative check: Equipment vendor literature and metallurgical handbooks often list electric-arc furnace hot-spot temperatures in the several-thousand-degree range, with 3000°C being a conventional reference point for maximum capability in MCQs. Why Other Options Are Wrong: 2000°C: Achievable, but not the upper bound.4500°C or 6000°C: Beyond typical industrial furnace practice and refractory limits; such temperatures relate to plasma/arc cores, not sustained furnace operation. Common Pitfalls: Confusing momentary arc column temperatures with usable furnace wall or charge temperatures. Ignoring refractory/electrode constraints that limit continuous operation. Final Answer: 3000

Question 8

Underfired furnace designs alter flame placement and gas circulation. Which of the following outcomes is not typically accomplished by an underfired arrangement?

Accepted Answer

Introduction / Context: In an underfired furnace, burners or firing ports direct flames and hot gases below or through passages such that heat reaches the underside of the charge. This improves uniformity and capacity compared with purely overfired layouts. The question asks which claimed benefit does not align with underfired principles. Given Data / Assumptions: Underfiring targets bottom heating to eliminate cold spots. Gas circulation can be arranged to protect edges/periphery from over-radiation. Capacity per floor area can rise due to improved heat transfer and reduced cycle time. Concept / Approach: Underfiring typically enhances effective gas temperature at the locations that matter for the load, increasing overall heat transfer rates. There is no inherent reduction in furnace-gas temperature; if anything, local gas temperatures at the charge surface may be higher or better directed. Therefore, “reduction in the temperature of furnace gases” is not a characteristic benefit of underfired designs. Step-by-Step Solution: List typical outcomes: remove bottom cold spot, protect edges, increase throughput per area.Evaluate the statement about lowering gas temperature: inconsistent with underfiring intent.Select it as the item not accomplished. Verification / Alternative check: Furnace retrofits introducing underfired or “twin-flame” concepts report improved uniformity and shorter cycles, not reductions in gas temperature; instead, they achieve better temperature distribution at the load surface. Why Other Options Are Wrong: Increase in capacity per area: Common via faster heating.Elimination of bottom cold spot: Primary design goal.Periphery protection: Achieved through flame pattern and baffling. Common Pitfalls: Equating “better heat use” with “lower gas temperature.” Efficiency improvements come from distribution and contact, not necessarily cooler gases. Ignoring that product temperature control depends on gas circulation design, not merely gas temperature magnitude. Final Answer: Reduction in the temperature of furnace gases.

Question 9

In burner trim and isolation service for gaseous fuels, the main gas valve in a fuel train is typically of which valve type (selected for good throttling and tight shutoff)?

Accepted Answer

Introduction / Context: Fuel trains for gaseous burners include regulators, safety shutoff valves, and a main control valve. Valve selection balances throttling characteristics, pressure drop, leakage class, and actuator compatibility. Knowing the typical choice helps in reading P&IDs and troubleshooting combustion systems. Given Data / Assumptions: The “main gas valve” is intended to modulate fuel flow for firing rate control and to close reliably under trip conditions (often paired with dedicated safety shutoff valves). Stable control around setpoints and good rangeability are important. The fluid is a clean gaseous fuel. Concept / Approach: Globe valves offer superior throttling characteristics due to their linear flow path change with stem position and well-defined flow coefficients. They provide finer control compared with on/off style gate valves and offer better modulation than basic butterfly valves at low openings. For many burner systems, the main control valve (modulating valve) is a globe valve equipped with a positioner/actuator, ensuring smooth firing-rate changes and stable pressure at the burner manifold. Step-by-Step Solution: Identify control objective: precise, repeatable modulation.Match valve characteristic: globe valves are preferred for accurate throttling.Conclude “globe” is the typical main gas control valve type. Verification / Alternative check: Combustion equipment specifications frequently call for globe control valves or specialized control ball valves; training schematics show globe valves on the modulating leg with safety shutoff valves upstream/downstream. Why Other Options Are Wrong: Gate: Good for isolation, poor for throttling—tends to chatter and erode seats.Butterfly: Economical and compact but less precise at low openings; commonly used for air, not always as the main fuel control.None of these: Incorrect because globe is a standard choice. Common Pitfalls: Assuming any valve with an actuator is suitable for precision control. Overlooking leakage class and safety certifications required in fuel service. Final Answer: globe

Question 10

In furnace operation, “overfire burning” refers to which characteristic phenomenon observed in the upper zones of the chamber?

Accepted Answer

Introduction / Context: Incomplete combustion near burners can leave combustible species, notably carbon monoxide and unburned hydrocarbons. In some furnaces, additional air admitted higher in the chamber completes oxidation above the primary combustion zone—a practice known as overfire air or overfire burning. Understanding this concept is important for emissions control and heat-release distribution. Given Data / Assumptions: Primary burners create a fuel-rich core or incomplete mixing near the flame root. Secondary (overfire) air ports are located higher along the gas path. Goal is to finish oxidation of CO and combustibles while managing temperature profiles and NOx. Concept / Approach: Overfire burning intentionally stages combustion. The first zone runs closer to stoichiometric or slightly fuel-rich to control peak temperatures and NOx. Further downstream, additional air promotes the oxidation of CO to CO2 and breakdown of hydrocarbons, shifting heat release away from the burner tile and providing better overall mixing. This is distinct from simply “supplying excess air” uniformly at the burners; the key is where the air is introduced and what it oxidizes in the upper zone. Step-by-Step Solution: Identify unburned species leaving primary zone (CO, VOCs).Recognize overfire air addition higher in the chamber.Define the phenomenon: completion of oxidation in the upper zone—overfire burning. Verification / Alternative check: Low-NOx furnace designs and many boiler firing systems employ overfire air (OFA) to reduce NOx and to complete burnout of CO at distance from the flame root. Why Other Options Are Wrong: Excess fuel: Leads to reducing conditions and high CO if not corrected; not the definition.Supply of excess air (generic): Too vague; the staged, upper-zone oxidation is the defining feature.None of these: Incorrect, because the staged upper-zone oxidation description is correct. Common Pitfalls: Confusing uniform high excess air with staged overfire air. Ignoring impacts on heat-transfer distribution and refractory hot spots when moving heat release upstream or downstream. Final Answer: burning carbon monoxide and other incombustible in upper zone of furnace by supplying more air.

Question 11

Reheating furnaces in steel plants: Which design is considered an improved, more fuel-efficient successor to the traditional pusher-type reheating furnace for heating slabs/billets prior to rolling?

Accepted Answer

Introduction / Context: Pusher-type reheating furnaces were common in older rolling mills, but modern steel plants favor designs that save fuel, reduce scale losses, and deliver tighter temperature uniformity. This question checks whether you can identify the evolved configuration that improves thermal efficiency and product quality while minimizing mechanical contact damage and skid marks. Given Data / Assumptions: The application is reheating steel slabs/billets/blooms before hot rolling. Key goals: better heat transfer, lower fuel consumption, reduced oxidation/scale, and smooth handling. “Improved and fuel efficient” refers to mainstream industrial practice, not niche or laboratory furnaces. Concept / Approach: A walking beam furnace lifts the workpiece off supports and “walks” it forward, alternating between stationary and advancing beams. By reducing continuous sliding, it cuts skid-mark cold spots, promotes more uniform soaking, and enables optimized combustion/recuperation. Higher heat-transfer effectiveness allows lower specific fuel use for the same throughput and exit temperature targets. Step-by-Step Solution: Identify drawbacks of pusher type: sliding abrasion, temperature non-uniformity, scale build-up, potential billet sticking.Match improved design: the walking beam mechanism lifts and conveys without dragging, improving temperature uniformity and surface quality.Link to efficiency: better exposure to hot gases and optimized zone control lower fuel per ton.Therefore, the correct choice is “Walking beam furnace”. Verification / Alternative check: Process heat texts and OEM catalogs consistently cite walking beam furnaces as the modern standard for high-productivity, fuel-efficient slab/billet reheating with excellent temperature homogeneity. Why Other Options Are Wrong: Shaft furnace: used for other materials and chemistries; not the mainstream reheating replacement.Tunnel kiln furnace: common for ceramics; not the standard for steel reheating lines.Rotary hearth furnace: suited for specific processes (e.g., DRI, forging stock), not the universal pusher successor.Walking hearth furnace: improves handling but the widely adopted efficiency upgrade is the walking beam variant. Common Pitfalls: Assuming any non-pusher system is the “upgrade.” The signature energy and quality benefits that displaced pushers in major mills are most closely associated with walking beam designs. Final Answer: Walking beam furnace

Question 12

Heat recovery hardware in furnaces/boilers: Which statement best describes a recuperator used for waste-heat recovery from hot flue gases?

Accepted Answer

Introduction / Context: High-temperature furnaces and boilers improve efficiency by reclaiming sensible heat from outgoing flue gases. Two broad families exist: recuperators and regenerators. Knowing the operating mode of each helps with correct specification and troubleshooting of efficiency shortfalls. Given Data / Assumptions: Hot flue gases are available from a process heater or furnace. Goal is preheating combustion air or another stream to cut fuel consumption. “Continuous” means heat is transferred without periodic flow reversal or storage cycles. Concept / Approach: A recuperator is a steady-flow heat exchanger (metallic or ceramic) that continuously transfers heat from hot flue gas to a cold stream (often combustion air). No checker-brick storage is involved. In contrast, a regenerator alternately stores heat in a thermal mass and then releases it after flow reversal, a cyclic process. Step-by-Step Solution: Identify the device that does not rely on cyclic storage: the recuperator.Recognize its function: continuous sensible-heat transfer across a barrier.Therefore, the correct description is “A continuous waste-heat recovery equipment”. Verification / Alternative check: Vendor datasheets classify recuperators under continuous service, while regenerators are documented with flow-reversal cycles and checkerwork descriptions. Why Other Options Are Wrong: Not used for fuel gas preheating: incorrect; recuperators frequently preheat combustion air and sometimes gaseous fuels where appropriate.Intermittent: that is the regenerator, not the recuperator.Heavier than a regenerator: generally the opposite for the same duty; regenerators are typically bulkier.Stores heat cyclically: definition of a regenerator, not a recuperator. Common Pitfalls: Confusing “recuperator” and “regenerator” because both reduce fuel use. The key distinction is continuous vs. cyclic operation. Final Answer: A continuous waste-heat recovery equipment

Question 13

Waste-heat uses in steam generators: In a thermal power plant, which equipment recover sensible heat from outgoing flue gases under normal operation?

Accepted Answer

Introduction / Context: Thermal power plants aim to extract as much useful energy as possible from fuel. Downstream of the furnace, heat-transfer surfaces recover waste heat from flue gases to raise efficiency. This question probes recognition of the multiple surfaces that benefit from the same flue-gas energy stream. Given Data / Assumptions: A boiler/steam generator with furnace, convection pass, and gas exit. Standard heat surfaces: economiser, superheater, and air preheater. Normal, steady firing without bypasses. Concept / Approach: The flue-gas sensible heat is used serially: the superheater elevates steam temperature above saturation; the economiser preheats feedwater; the air preheater warms combustion air. All three are positioned to tap the gas stream, subject to metallurgy and fouling constraints, thus all qualify as waste-heat recovery components. Step-by-Step Solution: Identify each exchanger’s duty that relies on flue gas: superheater (steam), economiser (feedwater), air preheater (combustion air).Confirm all take heat from the same gas path.Hence, select “All (a), (b) and (c)”. Verification / Alternative check: Typical boiler heat-balance diagrams show a cascade of heat transfer from hottest gases to superheater, then economiser, and finally air preheater before stack release. Why Other Options Are Wrong: Any subset omits a standard flue-gas-heated surface present in most utility boilers.Limiting to two devices ignores the superheater’s clear use of flue-gas heat. Common Pitfalls: Assuming “waste heat” only means low-grade heat. In boilers, even high-temperature superheaters are part of the same waste-heat recovery chain. Final Answer: All (a), (b) and (c)

Question 14

Gas flow through packed beds: Identify the furnace/process in which combustion/processing gases are deliberately drawn downward through the stock bed from below the grate or windbox.

Accepted Answer

Introduction / Context: Some thermal processes purposefully pull hot gases through a granular or lumpy bed to promote reactions and uniform heating. Recognizing the direction of gas flow is central to diagnosing air distribution, burn-through control, and bed permeability issues. Given Data / Assumptions: We consider classic ore sintering practice on a traveling grate. Gas handling involves induced-draft fans drawing gases through the bed. We compare this with other furnace types that do not employ strong down-draught through a particulate bed. Concept / Approach: On sintering machines, ignition is initiated at the top and powerful suction below the grate draws combustion air and hot gases downward, promoting bed consolidation (sinter). The pressure drop across the bed is an essential control variable. Soaking pits and beehive ovens do not follow this specific down-draught through a particulate bed arrangement. Step-by-Step Solution: Identify the process known for induced down-draught through ore/coke/fines: the sintering machine.Relate to equipment layout: windboxes and fans below the grate provide suction.Therefore, select “Sintering machine (down-draught sintering)”. Verification / Alternative check: Metallurgical process texts explicitly describe traveling-grate sintering with suction applied beneath the bed to control burn-through and productivity. Why Other Options Are Wrong: Soaking pit: heats ingots in a chamber; no downward suction through a loose bed.Beehive oven: coke ovens have different draft and flow patterns, not the sinter down-draught scheme.Rotary kiln: cross-/co-current flow in a rotating tube, not suction through a stationary packed bed. Common Pitfalls: Confusing any “draft” with “down-draught through a bed.” The sinter machine’s defining feature is suction through the granular layer. Final Answer: Sintering machine (down-draught sintering)

Question 15

Where does the heat go in a fired furnace? The split between heat absorbed by the charge/stock and the heat lost to furnace structure and flue gases depends primarily on which factors?

Accepted Answer

Introduction / Context: Furnace efficiency is the fraction of fuel energy delivered to the stock. Understanding what controls the split between useful absorption and losses helps engineers tune firing patterns, choose materials, and set operating modes for best performance. Given Data / Assumptions: A refractory-lined furnace heats a metallic or ceramic load. We consider steady, representative operation with proper combustion. Variables include firing rate, radiative properties, materials conductivities, and process scheduling. Concept / Approach: Higher firing rates and high-emissivity flames increase radiative transfer to the stock but can also raise flue losses if residence is short. The thermal conductivity of the stock and linings governs temperature gradients, warm-up time, and wall losses. Batch versus continuous operation changes transient losses, soak uniformity, and average wall temperatures—all of which affect efficiency. Step-by-Step Solution: Relate firing rate/emissivity to radiative heat flux to the charge.Account for material properties: conductive stock heats faster and more uniformly; refractory conductivity affects shell losses.Consider operating mode: batch cycles incur more start-stop and warm-up losses than well-loaded continuous systems.Therefore, all listed factors jointly determine the heat split. Verification / Alternative check: Heat-balance audits consistently vary with burner settings, charge properties, and production scheduling; efficiency improves when these are optimized together. Why Other Options Are Wrong: Any single factor alone is incomplete; real furnaces respond to combined thermal and operational parameters.Excess-air setting matters, but it is only one among several drivers. Common Pitfalls: Over-focusing on combustion tuning while ignoring stock properties or process cadence; capacity utilization and lining selection can shift losses dramatically. Final Answer: All (a), (b) and (c)

Question 16

Determinants of furnace capacity: Which variables most directly influence the achievable throughput (capacity) of a heating furnace?

Accepted Answer

Introduction / Context: “Capacity” is not just burner nameplate. The real limit is how fast heat can be transferred and absorbed to bring product to target temperature uniformly. This question highlights key thermal variables that set the pace of heating and, therefore, the achievable throughput. Given Data / Assumptions: A direct-fired or radiant-tube furnace heating metal or ceramic stock. We consider steady, tuned combustion. Heat transfer to and within the stock controls ramp-up and soak times. Concept / Approach: High flue-gas temperatures imply higher gas-to-surface temperature difference and radiative/convective driving force. Stock thermal conductivity governs how quickly surface heat penetrates to the core. Stock thickness sets the conduction path length; thicker sections need longer times to equalize temperature. All three therefore determine how many tons per hour can be processed to specification. Step-by-Step Solution: Connect flue-gas temperature with heat-transfer coefficients and driving force.Relate stock conductivity to internal temperature gradients during heating.Relate thickness to characteristic heating time ~ L^2/alpha (qualitative), where alpha is thermal diffusivity.Thus, capacity depends on all listed variables. Verification / Alternative check: Heating curves and soak calculations in design handbooks explicitly depend on material properties (k, rho, cp), section size, and furnace temperature profiles, corroborating the selection. Why Other Options Are Wrong: Only burner rating: insufficient; you cannot force heat into thick, low-conductivity parts arbitrarily fast without quality loss.Any single factor alone ignores the coupled nature of external and internal heat transfer. Common Pitfalls: Equating bigger burners with higher capacity; product heating limitations often dominate, especially for thick or low-k materials. Final Answer: All (a), (b) and (c).

Furnace Technology Questions