Q: Solid–liquid separation from slurries:\nWhich equipment is primarily used to separate coarse particles from a slurry containing fine particles?

Introduction / Context: Slurry processing often requires splitting a mixed particle-size distribution into coarse and fine fractions prior to grinding, flotation, or thickening. Different devices target different size ranges and cut sharpness. Understanding which unit prioritises coarse removal assists in designing crushing–classification circuits in minerals and chemical processing. Given Data / Assumptions: Feed is a slurry containing a wide size distribution. Goal is to remove or separate the coarse particles. Concept / Approach: Classifiers (e.g., rake, spiral) rely on gravity settling in a controlled flow to return coarse particles (sands) while allowing fines (slimes) to overflow. Hydrocyclones can make fine cuts but are often used for finer separations and can misplace coarse in some conditions. Thickeners concentrate fines by settling but are not designed as precise classifiers. Decanters remove liquid from slurry but provide limited size discrimination compared with dedicated classifiers. Step-by-Step Solution: Identify target: preferential removal of coarse solids.Match process: gravitational classification with rakes/spirals suits coarse splits.Choose “Classifiers.” Verification / Alternative check: Standard grinding circuits pair ball mills with spiral classifiers to close the loop on coarse recirculation, underscoring their role in coarse/fine separation. Why Other Options Are Wrong: Thickeners: concentrate fines but not designed for sharp coarse/fine classification. Hydrocyclones: often used for finer cut sizes; may be acceptable but not “primarily” for coarse removal in classic teaching. Decanters/clarifiers: focus on liquid–solid split, not selective coarse removal. Common Pitfalls: Assuming all settlers are equivalent; classifiers are tuned to size-based return/overflow duties. Final Answer: Classifiers

Q: General crushing equation exponent:\nBond’s crushing law is obtained from the general size-reduction equation by taking n = ________ with an infinite feed size.

Introduction / Context: Generalised comminution expressions can be specialised to the three classical laws by selecting an exponent n. Correctly recalling which exponent yields Bond’s law is important for applying work index correlations and for exam problems connecting theory to practice. Given Data / Assumptions: General form reduces to Bond by setting n to a specific value. Feed is considered infinitely large for the simplification. Concept / Approach: In the general size-reduction energy relation, Rittinger corresponds to n = 2, Kick to n = 1, and Bond to the intermediate exponent n = 1.5. With this selection and F → ∞, the Bond form E ∝ 1/√P emerges. Remembering the “middle” value 1.5 helps distinguish Bond’s theory from the surface-based (Rittinger) and size-ratio (Kick) forms. Step-by-Step Solution: Recall mapping: Kick n = 1; Bond n = 1.5; Rittinger n = 2.Apply Bond n = 1.5 with F → ∞.Conclude n = 1.5. Verification / Alternative check: Handbook derivations list Bond’s “third theory” explicitly with the 1.5 exponent, consistent with work index equations used in design. Why Other Options Are Wrong: n = 1: Kick’s law. n = 2: Rittinger’s law. n = 2.5 or 0.5: not used in the classical triad. Common Pitfalls: Memorising formulas without associating the corresponding exponent; use the mnemonic Kick(1), Bond(1.5), Rittinger(2). Final Answer: 1.5

Q: Vacuum filtration equipment identification:\nWhich of the following is a vacuum filter commonly used for continuous solid–liquid separation?

Introduction / Context: Industrial solid–liquid separation relies on vacuum, pressure, or centrifugal driving forces. Being able to name which devices are vacuum filters—and which are not—helps quickly shortlist equipment for continuous vs. batch duties, cake washing, and scale-up in minerals and chemicals processing. Given Data / Assumptions: We compare common devices used in practice. Continuous operation is often required at large throughput. Concept / Approach: Rotary disc (and rotary drum) filters are classic continuous vacuum filters: a rotating element carries sectors through filtration, washing, and drying zones under vacuum. Plate-and-frame filter presses operate in batch mode using pressure, not vacuum, while basket centrifuges use centrifugal force. Nutsch filters may be operated under vacuum or pressure in batch service; when operated by gravity only, they are not vacuum devices. Pressure leaf filters are pressure-driven, not vacuum-driven. Step-by-Step Solution: Identify which option explicitly names a vacuum device.Rotary disc vacuum filters provide continuous vacuum filtration.Select “Rotary disc vacuum filter.” Verification / Alternative check: Equipment manuals designate rotary drum/disc units as continuous vacuum filters with defined filtration, wash, and dry arcs of rotation. Why Other Options Are Wrong: Filter press/pressure leaf: pressure-driven batch or semi-continuous. Basket centrifuge: centrifugal, not vacuum. Nutsch (gravity-only): no vacuum applied. Common Pitfalls: Assuming “tank filter” always means vacuum; many Nutsch filters operate by gravity or pressure instead. Final Answer: Rotary disc vacuum filter

Q: Moore filter classification:\nIn industrial filtration terminology, a Moore filter is classified as which type of filter?

Introduction / Context: Specialised filter names (e.g., Oliver, Moore, Kelly) often indicate the mechanical layout or vendor lineage. Recognising the generic class behind a trade or legacy name helps engineers interpret legacy documentation and specify equivalent equipment during revamps or replacements. Given Data / Assumptions: The question references “Moore filter” as used in classic chemical engineering texts. We map it to its generic category. Concept / Approach: In conventional classifications, the Moore filter is referenced as a leaf-type filter: an assembly of perforated leaves covered with filter medium, connected to a common manifold, typically operated under vacuum for batch or semi-continuous cake formation and discharge. While rotary drum/disc filters are also vacuum devices, the Moore designation historically correlates with leaf configurations rather than a rotating drum or disc format, and not with plate-and-frame presses or granular sand filters. Step-by-Step Solution: Identify Moore as a legacy name tied to leaf constructions.Differentiate from rotary drum/disc and plate-and-frame geometries.Select “Leaf filter.” Verification / Alternative check: Older equipment catalogs and unit operations texts list Moore under leaf/vacuum leaf filters, distinct from Oliver rotary drums and standard presses. Why Other Options Are Wrong: Filter press: plate-and-frame pressure, not Moore’s typical configuration. Rotary vacuum filter: a different rotating geometry (Oliver/disc types). Sand filter/centrifugal screen: different driving forces and media. Common Pitfalls: Assuming any vacuum filter is rotary; many are stationary leaf assemblies. Final Answer: Leaf filter

Q: Particle geometry — shape factor:\nFor a right circular cylinder whose length equals its diameter, the shape factor (defined here as L/D) is:

Introduction / Context: “Shape factor” has several definitions in particle technology. In many quick MCQs, it is taken as a simple geometric ratio to characterise elongation or flatness—often length-to-diameter (L/D) for cylinders or rods. Being explicit about the definition avoids confusion with sphericity or surface/volume-based factors used elsewhere. Given Data / Assumptions: Shape factor is defined for this question as L/D. The cylinder has length L equal to diameter D. Concept / Approach: With the stated definition, shape factor = L/D. If L equals D, then L/D = 1. Other more advanced definitions (e.g., sphericity = surface area of sphere of equal volume divided by actual surface area) yield different numbers, but those are not invoked here. The key is to apply the provided or implied definition consistently. Step-by-Step Solution: Adopt definition: shape factor = L/D.Insert L = D into ratio.Compute: shape factor = 1.0. Verification / Alternative check: Dimensional checks confirm a dimensionless ratio equal to unity for a cylinder with equal length and diameter. Why Other Options Are Wrong: Values 0.5, 1.5, 2.0, 0.75 correspond to different L/D geometries (short disks or elongated rods), not L = D. Common Pitfalls: Mixing differing “shape factor” definitions; always confirm whether L/D, W/D, or sphericity is intended. Final Answer: 1.0

Q: Ball mill operation:\nRelative to the critical speed, how should the operating speed of a ball mill be chosen for efficient grinding?

Introduction / Context: Ball mills rely on cascading and cataracting of grinding media to produce impact and attrition on the charge. The critical speed is the rotational speed at which centrifugal force equals gravitational force on a mill charge at the shell, preventing media from falling. Understanding the relation between operating and critical speed is central to mill performance. Given Data / Assumptions: Critical speed N_c is defined for a given mill diameter. Grinding effectiveness requires media to fall and slide, not stick to the shell. Concept / Approach: Operating a ball mill below the critical speed (commonly 60–80% of N_c) promotes cascading and cataracting motions, enabling effective breakage. At or above N_c, media cling to the shell and cease to fall, drastically reducing grinding. Excessively low speeds can lead to poor lift and low energy input. Therefore, “less than the critical speed” is the correct qualitative choice. Step-by-Step Solution: Recall definition and consequences of N_c.Relate operating window: about 0.6–0.8 N_c for many mills.Select “less than the critical speed.” Verification / Alternative check: Mill manuals and plant practice confirm setpoints below N_c to obtain desired media trajectories and power draw characteristics. Why Other Options Are Wrong: Equal to or greater than N_c: media centrifuge; grinding drops sharply. “Much more than” or “slightly more than”: both imply centrifuging. Common Pitfalls: Confusing “critical” with “optimal”; optimal is typically a fraction of N_c, not at or above it. Final Answer: Less than the critical speed

Q: Rotary drum vacuum filter — vacuum application zones:\nIn a general continuous rotary drum vacuum filter, vacuum is applied in which zone(s)?

Introduction / Context: Continuous rotary drum vacuum filters divide a rotation into arcs for cake formation (filtration), washing, and dewatering/drying. The vacuum system is valved to apply suction to the sectors passing through these zones. Understanding which arcs are under vacuum is essential for troubleshooting throughput, wash efficiency, and cake dryness. Given Data / Assumptions: Standard drum filter with filtrate receiver and valved sectors. Three functional arcs: filtration, wash, and drying prior to discharge. Concept / Approach: Vacuum is fundamental in all three arcs: it draws slurry liquor through the medium to form cake (filtration), pulls wash liquor through the cake to displace mother liquor (washing), and continues to remove liquid by suction and evaporation assistance (drying). Only the cake discharge zone is valved off vacuum to allow gas blowback or mechanical discharge. Hence the correct answer is that vacuum is applied in filtering, washing, and drying zones. Step-by-Step Solution: Identify each arc and its purpose.Associate vacuum with fluid removal or displacement in each arc.Conclude all three arcs are under vacuum. Verification / Alternative check: Piping and instrumentation diagrams show rotary valve ports connected to vacuum headers across the filtration, wash, and dewatering sectors. Why Other Options Are Wrong: Limiting vacuum to a single zone neglects essential wash and drying operations. “None” contradicts the operating principle of vacuum filtration. Common Pitfalls: Assuming drying is purely evaporative; in drum filters it is largely vacuum-assisted drainage. Final Answer: All of the above: filtering, washing, and drying zones

Q: Baghouse resistance scaling:\nIn a bag filter, the additional resistance offered by the dust cake varies with dust concentration c and particle size s approximately as:

Introduction / Context: Pressure drop across a baghouse increases due to both the fabric and the growing dust cake. Qualitatively, finer particles pack more densely and build higher resistance per unit mass deposited; greater dust concentration causes the cake to build faster. This question probes the common proportionality used for quick reasoning in troubleshooting filtration systems. Given Data / Assumptions: c denotes dust concentration in the gas phase. s denotes a characteristic particle size. Other factors (air-to-cloth ratio, pulse cleaning) are held nominally constant. Concept / Approach: Smaller particles (lower s) produce more compact cakes with lower permeability, increasing resistance. Higher dust concentration (higher c) accelerates cake growth, also increasing resistance. A simple proportionality that captures both tendencies is resistance ∝ c/s: directly with concentration and inversely with particle size. While detailed models use Kozeny–Carman-type relations and porosity, the c/s scaling is a widely taught qualitative rule-of-thumb. Step-by-Step Solution: Relate cake permeability to particle size: finer → less permeable → higher resistance.Relate cake thickness growth rate to concentration: higher c → faster buildup.Combine into a simple proportionality: resistance ∝ c/s. Verification / Alternative check: Filtration handbooks present cake resistance proportional to mass deposited and inversely to a permeability term that increases with particle size, supporting the c/s logic qualitatively. Why Other Options Are Wrong: s/c or 1/(s·c): contradict observed trends for finer particles and higher concentrations. s·c: predicts larger particles increase resistance, contrary to practice. Independence: unrealistic for cake-dominated pressure drop. Common Pitfalls: Overinterpreting this proportionality as a rigorous design equation; it is a heuristic for quick troubleshooting. Final Answer: Proportional to c/s

Question 1

Mechanical conveyors — “scrapers” division:
Which of the following does NOT belong to the scraper-type conveyors group?

Accepted Answer

Introduction / Context: Scraper-type conveyors move bulk solids by dragging or scraping them along a trough using flights or chains. Knowing which common machines fall into this category helps in shortlisting equipment for sticky or granular materials, especially when horizontal or inclined transport is required inside process plants. Given Data / Assumptions: “Scraper” implies flights/drag elements contacting solids in a trough. We compare flight/drag devices against elevators and screw/ribbon devices. Concept / Approach: Flight and drag conveyors employ scrapers attached to chains to pull material along; these are archetypal scraper conveyors. Ribbon (helicoid) conveyors are a screw-conveyor variant and are not scraper-chain devices. Bucket elevators are vertical lifting machines using buckets on belts or chains and are not classified as scraper conveyors. Therefore, among the choices, the clear non-scraper is the bucket elevator. Step-by-Step Solution: Define scraper conveyors: flights/drag elements in a trough.Match each option to definition.Identify bucket elevator as a vertical lift device, not a scraper. Verification / Alternative check: Standard equipment taxonomies separate scraper/drag conveyors from elevators and screw conveyors in vendor catalogs and handbooks. Why Other Options Are Wrong: Flight conveyor: classic scraper. Drag conveyor: classic scraper (chain-drag). Ribbon conveyor: not a scraper but also not an elevator; still not the best answer vs. elevator. The bucket elevator is unequivocally non-scraper. Scraper chain in trough: definitionally a scraper. Common Pitfalls: Confusing screw and scraper mechanisms; screws convey by helical rotation rather than dragging with flights. Final Answer: Bucket elevator

Question 2

Agitation regimes in mixing:
During liquid agitation in a tank, the flow is said to be laminar when the agitator Reynolds number (Re) is in which range?

Accepted Answer

Introduction / Context: In mixing, the agitator Reynolds number Re = (rho * N * D^2) / mu indicates the flow regime, where rho is fluid density, N is rotational speed, D is impeller diameter, and mu is viscosity. Recognising the thresholds between laminar, transitional, and turbulent regimes guides impeller selection, power draw estimates, and scale-up strategies for reactors and blend tanks. Given Data / Assumptions: Re is defined for mechanically agitated vessels. We refer to the typical textbook thresholds. Concept / Approach: For mixing, laminar flow generally occurs for Re less than about 10; transitional behavior spans roughly Re 10 to 10^4 (depending on geometry), and turbulent flow dominates beyond that range. In the laminar regime, viscous forces dominate, streamlines are ordered, and power numbers vary inversely with Re. Thus, “Re < 10” is the accepted indicator of laminar mixing conditions for common impellers. Step-by-Step Solution: Recall definition of Re for mixing: Re = rho * N * D^2 / mu.Map standard thresholds: laminar < 10; transitional ~ 10–10^4; turbulent > 10^4.Select “< 10” as the laminar condition. Verification / Alternative check: Mixing handbooks and design correlations (e.g., power number vs. Re) show distinct asymptotes for Re below 10, consistent with laminar flow and predictable shear fields. Why Other Options Are Wrong: > 10 or > 100: move into transitional/turbulent domains. < 100: too loose; includes transitional region; the accepted laminar threshold is much lower (~10). Common Pitfalls: Applying pipe-flow Re thresholds directly to mixing; geometry and rotating flow change the numerical ranges. Final Answer: < 10

Question 3

Solid–liquid separation from slurries:
Which equipment is primarily used to separate coarse particles from a slurry containing fine particles?

Accepted Answer

Introduction / Context: Slurry processing often requires splitting a mixed particle-size distribution into coarse and fine fractions prior to grinding, flotation, or thickening. Different devices target different size ranges and cut sharpness. Understanding which unit prioritises coarse removal assists in designing crushing–classification circuits in minerals and chemical processing. Given Data / Assumptions: Feed is a slurry containing a wide size distribution. Goal is to remove or separate the coarse particles. Concept / Approach: Classifiers (e.g., rake, spiral) rely on gravity settling in a controlled flow to return coarse particles (sands) while allowing fines (slimes) to overflow. Hydrocyclones can make fine cuts but are often used for finer separations and can misplace coarse in some conditions. Thickeners concentrate fines by settling but are not designed as precise classifiers. Decanters remove liquid from slurry but provide limited size discrimination compared with dedicated classifiers. Step-by-Step Solution: Identify target: preferential removal of coarse solids.Match process: gravitational classification with rakes/spirals suits coarse splits.Choose “Classifiers.” Verification / Alternative check: Standard grinding circuits pair ball mills with spiral classifiers to close the loop on coarse recirculation, underscoring their role in coarse/fine separation. Why Other Options Are Wrong: Thickeners: concentrate fines but not designed for sharp coarse/fine classification. Hydrocyclones: often used for finer cut sizes; may be acceptable but not “primarily” for coarse removal in classic teaching. Decanters/clarifiers: focus on liquid–solid split, not selective coarse removal. Common Pitfalls: Assuming all settlers are equivalent; classifiers are tuned to size-based return/overflow duties. Final Answer: Classifiers

Question 4

Comminution theories — identify Bond’s law:
Which statement correctly characterises Bond’s crushing law in size reduction?

Accepted Answer

Introduction / Context: Comminution (crushing and grinding) power requirements are estimated using empirical laws: Kick’s law, Rittinger’s law, and Bond’s law. Each relates specific energy to a function of the size reduction ratio and is valid over a certain size range. Bond’s “third theory of comminution” is widely used for design correlations in crushing and milling circuits. Given Data / Assumptions: Feed is very large relative to product (the classic Bond simplification). Characteristic size is represented by a screen size such as 80% passing (F80, P80). Concept / Approach: Bond’s law states that the specific energy E is proportional to (1/√P) − (1/√F), where F and P are characteristic feed and product sizes. For very large feed (F → ∞), 1/√F → 0, so E ∝ 1/√P. In contrast, Rittinger’s law states E ∝ (1/P − 1/F), corresponding to new surface creation and exaggerating energy for very fine sizes; Kick’s law uses a logarithmic size ratio for coarse crushing. Thus the statement linking energy to the inverse square root of product size aligns with Bond’s law. Step-by-Step Solution: Recall Bond relation: E ∝ (1/√P − 1/√F).Simplify for very large F: E ∝ 1/√P.Select the statement expressing this dependence. Verification / Alternative check: Design handbooks use Bond work index W_i with E = W_i * (10/√P − 10/√F) for P, F in micrometres, reinforcing the inverse-square-root size dependence. Why Other Options Are Wrong: New surface proportionality (option d) is Rittinger’s law, not Bond’s. Independence from size (option e) contradicts all comminution theories. Option a’s comparison wording is ambiguous; Bond predicts less severe energy rise than Rittinger for very fine sizes but does not “call for” fine energy generically. Option b is too sweeping; Bond is widely applied in practice. Common Pitfalls: Confusing the three laws’ size ranges; Bond is intermediate between Kick and Rittinger. Final Answer: It states that energy required from very large feed is proportional to 1/sqrt(product size).

Question 5

General crushing equation exponent:
Bond’s crushing law is obtained from the general size-reduction equation by taking n = ________ with an infinite feed size.

Accepted Answer

Introduction / Context: Generalised comminution expressions can be specialised to the three classical laws by selecting an exponent n. Correctly recalling which exponent yields Bond’s law is important for applying work index correlations and for exam problems connecting theory to practice. Given Data / Assumptions: General form reduces to Bond by setting n to a specific value. Feed is considered infinitely large for the simplification. Concept / Approach: In the general size-reduction energy relation, Rittinger corresponds to n = 2, Kick to n = 1, and Bond to the intermediate exponent n = 1.5. With this selection and F → ∞, the Bond form E ∝ 1/√P emerges. Remembering the “middle” value 1.5 helps distinguish Bond’s theory from the surface-based (Rittinger) and size-ratio (Kick) forms. Step-by-Step Solution: Recall mapping: Kick n = 1; Bond n = 1.5; Rittinger n = 2.Apply Bond n = 1.5 with F → ∞.Conclude n = 1.5. Verification / Alternative check: Handbook derivations list Bond’s “third theory” explicitly with the 1.5 exponent, consistent with work index equations used in design. Why Other Options Are Wrong: n = 1: Kick’s law. n = 2: Rittinger’s law. n = 2.5 or 0.5: not used in the classical triad. Common Pitfalls: Memorising formulas without associating the corresponding exponent; use the mnemonic Kick(1), Bond(1.5), Rittinger(2). Final Answer: 1.5

Question 6

Vacuum filtration equipment identification:
Which of the following is a vacuum filter commonly used for continuous solid–liquid separation?

Accepted Answer

Introduction / Context: Industrial solid–liquid separation relies on vacuum, pressure, or centrifugal driving forces. Being able to name which devices are vacuum filters—and which are not—helps quickly shortlist equipment for continuous vs. batch duties, cake washing, and scale-up in minerals and chemicals processing. Given Data / Assumptions: We compare common devices used in practice. Continuous operation is often required at large throughput. Concept / Approach: Rotary disc (and rotary drum) filters are classic continuous vacuum filters: a rotating element carries sectors through filtration, washing, and drying zones under vacuum. Plate-and-frame filter presses operate in batch mode using pressure, not vacuum, while basket centrifuges use centrifugal force. Nutsch filters may be operated under vacuum or pressure in batch service; when operated by gravity only, they are not vacuum devices. Pressure leaf filters are pressure-driven, not vacuum-driven. Step-by-Step Solution: Identify which option explicitly names a vacuum device.Rotary disc vacuum filters provide continuous vacuum filtration.Select “Rotary disc vacuum filter.” Verification / Alternative check: Equipment manuals designate rotary drum/disc units as continuous vacuum filters with defined filtration, wash, and dry arcs of rotation. Why Other Options Are Wrong: Filter press/pressure leaf: pressure-driven batch or semi-continuous. Basket centrifuge: centrifugal, not vacuum. Nutsch (gravity-only): no vacuum applied. Common Pitfalls: Assuming “tank filter” always means vacuum; many Nutsch filters operate by gravity or pressure instead. Final Answer: Rotary disc vacuum filter

Question 7

Moore filter classification:
In industrial filtration terminology, a Moore filter is classified as which type of filter?

Accepted Answer

Introduction / Context: Specialised filter names (e.g., Oliver, Moore, Kelly) often indicate the mechanical layout or vendor lineage. Recognising the generic class behind a trade or legacy name helps engineers interpret legacy documentation and specify equivalent equipment during revamps or replacements. Given Data / Assumptions: The question references “Moore filter” as used in classic chemical engineering texts. We map it to its generic category. Concept / Approach: In conventional classifications, the Moore filter is referenced as a leaf-type filter: an assembly of perforated leaves covered with filter medium, connected to a common manifold, typically operated under vacuum for batch or semi-continuous cake formation and discharge. While rotary drum/disc filters are also vacuum devices, the Moore designation historically correlates with leaf configurations rather than a rotating drum or disc format, and not with plate-and-frame presses or granular sand filters. Step-by-Step Solution: Identify Moore as a legacy name tied to leaf constructions.Differentiate from rotary drum/disc and plate-and-frame geometries.Select “Leaf filter.” Verification / Alternative check: Older equipment catalogs and unit operations texts list Moore under leaf/vacuum leaf filters, distinct from Oliver rotary drums and standard presses. Why Other Options Are Wrong: Filter press: plate-and-frame pressure, not Moore’s typical configuration. Rotary vacuum filter: a different rotating geometry (Oliver/disc types). Sand filter/centrifugal screen: different driving forces and media. Common Pitfalls: Assuming any vacuum filter is rotary; many are stationary leaf assemblies. Final Answer: Leaf filter

Question 8

Particle geometry — shape factor:
For a right circular cylinder whose length equals its diameter, the shape factor (defined here as L/D) is:

Accepted Answer

Introduction / Context: “Shape factor” has several definitions in particle technology. In many quick MCQs, it is taken as a simple geometric ratio to characterise elongation or flatness—often length-to-diameter (L/D) for cylinders or rods. Being explicit about the definition avoids confusion with sphericity or surface/volume-based factors used elsewhere. Given Data / Assumptions: Shape factor is defined for this question as L/D. The cylinder has length L equal to diameter D. Concept / Approach: With the stated definition, shape factor = L/D. If L equals D, then L/D = 1. Other more advanced definitions (e.g., sphericity = surface area of sphere of equal volume divided by actual surface area) yield different numbers, but those are not invoked here. The key is to apply the provided or implied definition consistently. Step-by-Step Solution: Adopt definition: shape factor = L/D.Insert L = D into ratio.Compute: shape factor = 1.0. Verification / Alternative check: Dimensional checks confirm a dimensionless ratio equal to unity for a cylinder with equal length and diameter. Why Other Options Are Wrong: Values 0.5, 1.5, 2.0, 0.75 correspond to different L/D geometries (short disks or elongated rods), not L = D. Common Pitfalls: Mixing differing “shape factor” definitions; always confirm whether L/D, W/D, or sphericity is intended. Final Answer: 1.0

Question 9

Ball mill operation:
Relative to the critical speed, how should the operating speed of a ball mill be chosen for efficient grinding?

Accepted Answer

Introduction / Context: Ball mills rely on cascading and cataracting of grinding media to produce impact and attrition on the charge. The critical speed is the rotational speed at which centrifugal force equals gravitational force on a mill charge at the shell, preventing media from falling. Understanding the relation between operating and critical speed is central to mill performance. Given Data / Assumptions: Critical speed N_c is defined for a given mill diameter. Grinding effectiveness requires media to fall and slide, not stick to the shell. Concept / Approach: Operating a ball mill below the critical speed (commonly 60–80% of N_c) promotes cascading and cataracting motions, enabling effective breakage. At or above N_c, media cling to the shell and cease to fall, drastically reducing grinding. Excessively low speeds can lead to poor lift and low energy input. Therefore, “less than the critical speed” is the correct qualitative choice. Step-by-Step Solution: Recall definition and consequences of N_c.Relate operating window: about 0.6–0.8 N_c for many mills.Select “less than the critical speed.” Verification / Alternative check: Mill manuals and plant practice confirm setpoints below N_c to obtain desired media trajectories and power draw characteristics. Why Other Options Are Wrong: Equal to or greater than N_c: media centrifuge; grinding drops sharply. “Much more than” or “slightly more than”: both imply centrifuging. Common Pitfalls: Confusing “critical” with “optimal”; optimal is typically a fraction of N_c, not at or above it. Final Answer: Less than the critical speed

Question 10

Rotary drum vacuum filter — vacuum application zones:
In a general continuous rotary drum vacuum filter, vacuum is applied in which zone(s)?

Accepted Answer

Introduction / Context: Continuous rotary drum vacuum filters divide a rotation into arcs for cake formation (filtration), washing, and dewatering/drying. The vacuum system is valved to apply suction to the sectors passing through these zones. Understanding which arcs are under vacuum is essential for troubleshooting throughput, wash efficiency, and cake dryness. Given Data / Assumptions: Standard drum filter with filtrate receiver and valved sectors. Three functional arcs: filtration, wash, and drying prior to discharge. Concept / Approach: Vacuum is fundamental in all three arcs: it draws slurry liquor through the medium to form cake (filtration), pulls wash liquor through the cake to displace mother liquor (washing), and continues to remove liquid by suction and evaporation assistance (drying). Only the cake discharge zone is valved off vacuum to allow gas blowback or mechanical discharge. Hence the correct answer is that vacuum is applied in filtering, washing, and drying zones. Step-by-Step Solution: Identify each arc and its purpose.Associate vacuum with fluid removal or displacement in each arc.Conclude all three arcs are under vacuum. Verification / Alternative check: Piping and instrumentation diagrams show rotary valve ports connected to vacuum headers across the filtration, wash, and dewatering sectors. Why Other Options Are Wrong: Limiting vacuum to a single zone neglects essential wash and drying operations. “None” contradicts the operating principle of vacuum filtration. Common Pitfalls: Assuming drying is purely evaporative; in drum filters it is largely vacuum-assisted drainage. Final Answer: All of the above: filtering, washing, and drying zones

Question 11

Baghouse resistance scaling:
In a bag filter, the additional resistance offered by the dust cake varies with dust concentration c and particle size s approximately as:

Accepted Answer

Introduction / Context: Pressure drop across a baghouse increases due to both the fabric and the growing dust cake. Qualitatively, finer particles pack more densely and build higher resistance per unit mass deposited; greater dust concentration causes the cake to build faster. This question probes the common proportionality used for quick reasoning in troubleshooting filtration systems. Given Data / Assumptions: c denotes dust concentration in the gas phase. s denotes a characteristic particle size. Other factors (air-to-cloth ratio, pulse cleaning) are held nominally constant. Concept / Approach: Smaller particles (lower s) produce more compact cakes with lower permeability, increasing resistance. Higher dust concentration (higher c) accelerates cake growth, also increasing resistance. A simple proportionality that captures both tendencies is resistance ∝ c/s: directly with concentration and inversely with particle size. While detailed models use Kozeny–Carman-type relations and porosity, the c/s scaling is a widely taught qualitative rule-of-thumb. Step-by-Step Solution: Relate cake permeability to particle size: finer → less permeable → higher resistance.Relate cake thickness growth rate to concentration: higher c → faster buildup.Combine into a simple proportionality: resistance ∝ c/s. Verification / Alternative check: Filtration handbooks present cake resistance proportional to mass deposited and inversely to a permeability term that increases with particle size, supporting the c/s logic qualitatively. Why Other Options Are Wrong: s/c or 1/(s·c): contradict observed trends for finer particles and higher concentrations. s·c: predicts larger particles increase resistance, contrary to practice. Independence: unrealistic for cake-dominated pressure drop. Common Pitfalls: Overinterpreting this proportionality as a rigorous design equation; it is a heuristic for quick troubleshooting. Final Answer: Proportional to c/s

Question 12

Rittinger’s number and grindability:
Rittinger’s number denotes new surface area created per unit mechanical energy during grinding. A larger Rittinger’s number implies:

Accepted Answer

Introduction / Context: Grinding performance can be discussed in terms of how effectively energy is converted into new surface area. Rittinger’s law asserts that energy is proportional to new surface created; therefore, a material that generates more surface per unit energy is “easier” to grind to fine sizes, and this is captured by Rittinger’s number. Given Data / Assumptions: Rittinger’s number increases with surface area generated per unit energy. We compare relative grindability across materials at similar conditions. Concept / Approach: If Rittinger’s number is high, each kilowatt-hour of input yields a larger increase in surface area. That means, for a given target fineness, less energy is needed—i.e., the material is more amenable to grinding. Conversely, a low Rittinger’s number suggests that more energy is required to create the same surface area, indicating poor grindability. Step-by-Step Solution: Connect definition: number ∝ surface produced per energy.Infer implication: higher value → better surface generation efficiency.Conclude “easier grindability.” Verification / Alternative check: Comparative milling studies frequently report materials with high friability achieving target fineness at lower specific energy, consistent with higher Rittinger’s numbers. Why Other Options Are Wrong: Poor grindability/higher power: contradict the definition. No relation: incorrect because Rittinger’s number explicitly ties surface to energy. Particle sphericity: unrelated to this metric. Common Pitfalls: Confusing Rittinger’s number with Bond work index; the former relates to surface creation per energy, the latter to specific energy scaling with size reduction. Final Answer: Easier grindability (more surface created per energy input)

Question 13

Filtration modeling for cake flow:
The flow of filtrate through the cake in a plate-and-frame filter press is best described by which equation?

Accepted Answer

Introduction / Context: Designing filtration cycles requires a model for flow through porous cakes. While Darcy’s law provides the macroscopic relation, permeability correlations such as Kozeny–Carman link permeability to particle size and porosity, enabling engineering estimates of pressure drop/flow relationships in cake filtration, especially in plate-and-frame presses. Given Data / Assumptions: Laminar flow through a homogeneous porous cake. Filter cake properties characterised by porosity and specific surface. Concept / Approach: The Kozeny–Carman equation refines Darcy’s law by expressing permeability k in terms of particle size and porosity (k ∝ ε^3 / [S_v^2 * (1 − ε)^2]). This is appropriate for packed beds and filter cakes comprising small particles. Hagen–Poiseuille describes laminar flow in a single capillary tube, not a tortuous porous medium; Fanning and Bernoulli relate to pipe flows; Kremser is for gas absorption design, unrelated to filtration. Step-by-Step Solution: Identify flow regime: viscous, through porous cake.Select porous-media correlation: Kozeny–Carman.Reject single-tube and pipe-flow/absorption relations. Verification / Alternative check: Filtration textbooks derive cycle-time equations using Darcy’s law plus Kozeny–Carman to relate cake resistance to particle size and porosity. Why Other Options Are Wrong: Hagen–Poiseuille/Fanning/Bernoulli: apply to pipe/capillary flows, not porous cakes. Kremser: absorption tower stage analysis, not filtration. Common Pitfalls: Treating a porous cake as a single large capillary; real cakes exhibit tortuosity that Kozeny–Carman accounts for empirically. Final Answer: Kozeny–Carman equation

Question 14

Specific energy for crushing:
The energy consumed for crushing one ton of material typically lies in which range (kWh per ton)?

Accepted Answer

Introduction / Context: Order-of-magnitude energy estimates help evaluate equipment sizing and operating costs during preliminary design. Crushing (coarse size reduction) typically consumes less energy per ton than fine grinding, yet values vary with material hardness, feed size, and desired product size. This question assesses familiarity with the commonly quoted range for coarse crushing. Given Data / Assumptions: We refer to coarse/intermediate crushing, not fine grinding. Materials of typical hardness (not extremes). Concept / Approach: Textbook ranges place crushing energy roughly in the low single-digit kWh/ton bracket. Values around 2–3.5 kWh/ton are often quoted for jaw and gyratory crushing to mill feed sizes. Significantly lower figures (0.01–0.1 kWh/ton) are unrealistic for industrial crushers; much higher values (10–20 kWh/ton) align more with fine grinding/ultrafine milling. Therefore, the best representative range is 2.0 to 3.5 kWh/ton for general crushing energy estimates. Step-by-Step Solution: Recall typical energy tiers: crushing < grinding.Select mid-single-digit kWh/ton range for crushers.Choose 2.0–3.5 kWh/ton as representative. Verification / Alternative check: Plant surveys and handbooks report comminution balances consistent with this order-of-magnitude for primary/secondary crushing stages. Why Other Options Are Wrong: 0.01–0.1: far too low; ignores breakage work. 0.5–1.5: may apply in rare, very soft cases; generally low for design. 4–5 or 10–20: trend toward grinding rather than crushing. Common Pitfalls: Confusing mill grinding power (often >10 kWh/ton) with primary crushing requirements. Final Answer: 2.0 to 3.5 kWh/ton

Question 15

Agitator design — role of baffles:
Installing baffles in a mixing tank primarily helps to minimise which undesirable hydrodynamic tendencies?

Accepted Answer

Introduction / Context: Unbaffled, cylindrical tanks often develop strong swirling flow and a central vortex under top-entry agitation, which reduces mixing efficiency and can entrain air. Baffles are vertical strips fixed to the wall to disrupt swirling and promote top-to-bottom circulation and turbulence where appropriate. Given Data / Assumptions: Standard baffled tank with 4 radial baffles is considered. Newtonian liquids without yield stress. Concept / Approach: Baffles break tangential flow, converting rotational motion into radial and axial components, suppressing global swirl and the formation of a deep vortex. This improves power transfer from the impeller to the bulk liquid and enhances mixing, gas dispersion (when present), and heat transfer. Thus, they minimise both swirling and vortexing simultaneously. Step-by-Step Solution: Identify problems in unbaffled tanks: swirl and vortex.Introduce baffles to add flow resistance in the tangential direction.Conclude both phenomena are mitigated. Verification / Alternative check: Mixing correlations (power number, blend time) are specified for baffled tanks; unbaffled tanks show distinct, less efficient hydrodynamics with vortex formation. Why Other Options Are Wrong: Picking only one neglects the coupled nature of swirl and vortex. “Neither” contradicts the primary purpose of baffles. Cavitation relates to local pressure drops at impellers and is not the main reason for wall baffles. Common Pitfalls: Undersized or mispositioned baffles will not adequately suppress vortexing; typical width is about 1/12 of tank diameter. Final Answer: Both (a) and (b)

Question 16

Mineral processing terminology:
The crushed material sent to a separation unit is called the feed or ________.

Accepted Answer

Introduction / Context: In ore dressing and coal preparation, standard terms describe material streams: feed, concentrate, tailings, and middlings. Familiarity with this vocabulary is necessary to read flowsheets, material balance tables, and plant reports without ambiguity. Given Data / Assumptions: We refer to classic mineral processing nomenclature. The stream in question is the incoming material to a separator. Concept / Approach: The incoming stream is “feed,” often also called “heads” or “heading” in some texts. “Concentrate” denotes the valuable product with enriched mineral content; “tailings” are the waste fraction; “middlings” are intermediate-grade streams that may require recycle. Therefore, the term that pairs with feed in this context is heads/heading. Step-by-Step Solution: Identify the stream position: input to separation → feed.Recall synonym: feed ≈ heads/heading.Select “Heading (heads).” Verification / Alternative check: Historical flotation and gravity separation literature commonly uses “heads” analysis to denote the feed assay, in contrast to concentrate and tailings assays. Why Other Options Are Wrong: Tailing: waste output. Concentrate: valuable product. Middling: intermediate grade requiring retreatment. Refuse: generic waste, not the feed stream. Common Pitfalls: Mixing up “head grade” (feed assay) with “concentrate grade,” leading to incorrect recovery calculations. Final Answer: Heading (heads)

Question 17

Fine particulate control below dew point:
For removing submicron dust (< 1 µm) from air that is below its dew point, which equipment is most suitable?

Accepted Answer

Introduction / Context: Capturing very fine particulates from gas streams requires high-efficiency devices. Gas temperature relative to dew point affects equipment selection due to condensation risks. This item tests recognition of the device that combines high fine-particle efficiency with tolerance for saturated conditions when properly designed. Given Data / Assumptions: Particle size: less than 1 micrometre. Gas temperature: at or below dew point (saturated conditions). Industrial-scale removal is required. Concept / Approach: Electrostatic precipitators (ESPs) excel at collecting submicron particles by imparting charge and using an electric field to drive them to collection plates. While fabric filters also capture fines well, operation below dew point risks condensation on bags, blinding, and corrosion. Cyclones and settling chambers are ineffective for submicron particles. Wet scrubbers remove fines less efficiently without special enhancements and may face plume and wastewater issues. Properly designed ESPs (including wet ESPs when handling saturated/corrosive gas) are preferred for submicron control in saturated conditions. Step-by-Step Solution: Eliminate inertial devices (cyclone, settling) for submicron dust.Assess fabric filters: excellent dry, but dew-point operation risks blinding.Select electrostatic precipitator; wet ESP variant suits saturated gas. Verification / Alternative check: Air pollution control texts specify ESPs—especially wet ESPs—for fine mists and submicron particulates in saturated streams, such as acid mists and SO3 aerosols. Why Other Options Are Wrong: Bag filter: vulnerable to condensation; not ideal below dew point. Cyclone/settling chamber: poor efficiency at < 1 µm. Wet scrubber: may need very high energy (venturi) to approach ESP efficiency. Common Pitfalls: Ignoring dew-point effects on baghouses; saturated gas can rapidly foul filters. Final Answer: Electrostatic precipitator

Question 18

Cement finish grinding:
Cement clinker is typically reduced to fine powder predominantly by which mill?

Accepted Answer

Introduction / Context: Cement manufacture ends with finish grinding, where clinker and gypsum are ground to a fine powder. Traditional plants use long, compartmentalised ball mills—commonly called tube mills—for this duty, sometimes in combination with high-efficiency separators. Recognising this classic equipment choice is common in plant operations exams. Given Data / Assumptions: We refer to conventional (non-HPGR) circuits. Final product fineness is cement powder (Blaine in hundreds of m^2/kg). Concept / Approach: A tube mill is essentially an elongated ball mill with multiple compartments for coarse and fine grinding stages, optimised for clinker grinding. Crushers (roll/hammer) perform coarse size reduction of raw materials or clinker prior to milling; they cannot achieve cement fineness. Modern plants may use roller presses with ball mills, but the classical answer remains the tube mill for finish grinding. Step-by-Step Solution: Identify required fineness: far beyond crusher capability.Match to equipment engineered for fine grinding: tube (ball) mill.Select “Tube mill.” Verification / Alternative check: Process flow diagrams of legacy cement plants show tube mills with separators as the standard finishing step. Why Other Options Are Wrong: Roll/hammer crushers: pre-grinding/coarse crushing only. Ball mill (short): can be used, but the industry-specific term for clinker finish grinding is tube mill (long ball mill with compartments). Pin mill: used for soft chemicals, not clinker. Common Pitfalls: Equating any “ball mill” with the cement-specific “tube mill;” the latter is the recognised configuration for finish grinding. Final Answer: Tube mill (long ball mill)

Question 19

Function of a ball mill:
In comminution, a ball mill is primarily used for which mode of size reduction?

Accepted Answer

Introduction / Context: Different mills operate effectively over different size ranges. Recognising that ball mills are designed to reduce mill feed to fine powders using a combination of impact and attrition is fundamental when selecting equipment for a grinding circuit or interpreting plant data sheets and P&IDs. Given Data / Assumptions: Ball mill equipped with steel balls as grinding media. Operated below critical speed to promote cascading/cataracting. Concept / Approach: Ball mills handle feed sizes typically below 25 mm and deliver product fine enough for downstream classification or finish requirements (e.g., cement, mineral liberation). The mechanism involves both impact (media dropping) and attrition (sliding), producing fine grinding. Crushing is achieved by jaw, gyratory, and cone crushers at larger sizes; coarse grinding may be handled by rod mills or SAG mills depending on circuit design. Step-by-Step Solution: Identify typical feed/product sizes for ball mills.Match mechanisms (impact + attrition) to fine grinding role.Select “Fine grinding.” Verification / Alternative check: Comminution flow sheets routinely list ball mills in the fine grinding stage following primary/secondary crushing and sometimes rod milling or SAG milling. Why Other Options Are Wrong: Crushing: upstream, not a ball mill function. Coarse grinding only: ball mills excel at finer reductions. Pure attrition: impact is also significant. Cutting: unrelated to tumbling mills. Common Pitfalls: Overlapping rod and ball mill roles; rod mills better suit coarser, more uniform product with fewer fines. Final Answer: Fine grinding

Question 20

In industrial rubber processing, which mixer is most appropriate for devulcanising rubber scrap as well as preparing water dispersions and rubber solutions (clarify the specific unit used for such reclaim and solution-making tasks)?

Accepted Answer

Introduction / Context: This question targets practical equipment selection in rubber technology and mechanical operations. Different mixers serve distinct purposes: compounding, dispersion, solution preparation, and in some legacy processes, aiding devulcanisation or reclaiming scrap. Identifying the correct unit improves process efficiency and product quality. Given Data / Assumptions: Task includes devulcanisation (reclaim) of rubber scrap. Task also includes making water dispersions and rubber solutions. Equipment names refer to common industry terminology. Concept / Approach: Banbury mixers and sigma kneaders are intensive compounders for mastication and filler incorporation but are not the classical choice for dispersion-in-liquid or solution-making. Ribbon blenders and tumblers are gentle bulk mixers suited to dry blending. A pan-type muller (muller mixer) is a grinding-cum-mixing unit historically used for pigment dispersion, pastes, slurries, and reclaim operations in rubber—well aligned with dispersion and solution preparation for rubber reprocessing contexts. Step-by-Step Solution: List candidate mixers and their typical applications.Match requirements: dispersion in liquid media and legacy devulcanisation/reclaim operations.Identify muller as the most appropriate traditional choice. Verification / Alternative check: Process manuals describe muller/pan mixers for slurry, paste, and reclaim preparations where grinding plus mixing is needed, supporting their use in such rubber operations. Why Other Options Are Wrong: Tumbler / Ribbon blender: inadequate shear for dispersion or reclaim.Banbury mixer: excellent for compounding, not ideal for solution-making.Sigma mixer: good for dough-like masses, less suited to water dispersions/solutions compared with muller. Common Pitfalls: Assuming any high-shear compounding mixer is also optimal for liquid dispersion tasks. Final Answer: Muller

Mechanical Operations Questions