Question 1

Identify the incorrect statement about water treatment and boiler feedwater quality for high-pressure steam systems.

Accepted Answer

Introduction / Context: High-pressure boilers are sensitive to corrosion, deposition, and carryover. Proper feedwater conditioning and accurate understanding of microbiological control are essential to protect tubes, drums, and steam turbines. Given Data / Assumptions: High-pressure steam generation (e.g., power plant service). Attention to oxygen, alkalinity, and silica limits. Knowledge of microbial survivability under cold conditions. Concept / Approach: Caustic embrittlement is associated with excessive localized alkalinity (high NaOH) causing intergranular cracking. Silica tolerances drop sharply with pressure because silica volatilizes and deposits in turbines. Dissolved oxygen must be minimized (deaeration plus scavengers). Freezing/cooling does not guarantee pathogen kill; many microbes survive low temperatures and revive when warmed. Step-by-Step Solution: Evaluate each statement with boiler chemistry principles and microbiology.(a) True: high NaOH promotes embrittlement in stressed zones.(c) True: higher pressures demand lower silica to prevent carryover and turbine fouling.(d) True: dissolved oxygen must be near zero to avoid pitting corrosion.(b) False: low temperature preserves many bacteria; it is not a reliable disinfection method. Verification / Alternative check: Industry standards (e.g., power-plant chemistry guidelines) prescribe stringent oxygen and silica limits and recognize that disinfection requires heat or chemical methods, not cold storage. Why Other Options Are Wrong: They are technically correct best practices; only the claim that cooling/freezing “kills bacteria” is incorrect. Common Pitfalls: Assuming low temperature equals sterilization; ignoring oxygen ingress in condensate returns; neglecting silica monitoring at high pressure. Final Answer: Cooling and freezing of water reliably kill the bacteria present.

Question 2

Ambient air quality: an approximate tolerable limit for nitrogen oxides (as NOx, expressed as NO2) in air is closest to which value (ppm)?

Accepted Answer

Introduction / Context: Nitrogen oxides (NO and NO2, collectively NOx) are key urban air pollutants that contribute to ozone formation, smog, and respiratory irritation. Regulatory limits are typically set in parts per million (ppm) or micrograms per cubic meter for different averaging periods. Given Data / Assumptions: We seek an approximate, representative “tolerable” ambient concentration. Context is environmental air (not occupational exposure limits). Conventional textbook/entrance-exam benchmarks are referenced. Concept / Approach: Ambient standards around the world generally cap NO2 in the vicinity of tenths of a ppm for short-term averages, and much lower for annual means. Values like 1, 5, or 25 ppm are far above typical ambient targets and align more with short-term occupational exposure ceilings, not public air-quality criteria. Step-by-Step Solution: Recognize that 0.1 ppm corresponds to about 188–200 µg/m^3 for NO2, consistent with short-term ambient guidelines used historically in several jurisdictions.Compare options: 1 ppm (≈ 1,880 µg/m^3) and higher are excessive for ambient air.Select the closest acceptable ambient reference: 0.1 ppm. Verification / Alternative check: While exact standards vary by country and by averaging period, educational references often cite 0.1 ppm as a representative order-of-magnitude limit for NO2 in ambient air on a short-term basis. Why Other Options Are Wrong: 1, 5, and 25 ppm are much higher than typical ambient limits and would represent unhealthy air quality. Common Pitfalls: Confusing occupational exposure limits with ambient public-health standards; ignoring averaging time when comparing ppm values. Final Answer: 0.1

Question 3

For feedwater used in high-pressure boilers and steam turbines, which impurity is generally considered the most damaging due to carryover and deposition risks?

Accepted Answer

Introduction / Context: High-pressure boilers and turbines demand ultrapure water to prevent corrosion, scaling, and deposition. Among common impurities, silica poses unique challenges because it can volatilize with steam and deposit on turbine blades, severely degrading efficiency. Given Data / Assumptions: High-pressure service where steam purity requirements are stringent. Boiler drum and turbine susceptible to carryover effects. Comparison among typical impurities. Concept / Approach: Silica forms hard, glassy deposits that are very difficult to remove. At high pressures, silica’s volatility increases, enabling it to travel with steam and foul superheaters and turbine stages. While dissolved oxygen is corrosive, modern deaeration/scavenging can reduce O2 to near zero; silica control requires deep demineralization and close monitoring. Step-by-Step Solution: Identify deposition risk: silica deposits reduce heat transfer and turbine efficiency.Consider removal methods: strong-base anion exchange, mixed-bed polishers, or reverse osmosis plus polishing.Conclude that silica is the most detrimental impurity for high-pressure steam systems. Verification / Alternative check: Industry water-chemistry guidelines set silica limits that become extremely low as pressure rises, reflecting its outsized damage potential in turbines. Why Other Options Are Wrong: Turbidity: largely removed by clarification/filtration and does not carry over as silica does. Phenol: an organic contaminant of concern for emissions/odor, not primary for turbine scaling. Dissolved oxygen: critical for corrosion but manageable with deaeration and scavengers. Common Pitfalls: Assuming oxygen is always the worst impurity; at high pressures, silica is the key limiting constituent for steam purity. Final Answer: Silica

Question 4

Air pollution classification: which of the following is a secondary air pollutant formed in the atmosphere rather than emitted directly from a stack?

Accepted Answer

Introduction / Context: Air pollutants are categorized as primary (emitted directly) or secondary (formed in the atmosphere by chemical reactions). Identifying secondary pollutants helps target precursor controls and effective abatement strategies. Given Data / Assumptions: Typical urban atmosphere with sunlight, VOCs, and NOx. Understanding of smog formation chemistry. Concept / Approach: Photochemical smog forms when volatile organic compounds (VOCs) react with nitrogen oxides under sunlight, producing oxidants like ozone, peroxyacyl nitrates, and aldehydes. This mixture is not directly emitted; it arises from atmospheric photochemistry, hence it is a secondary pollutant complex. Step-by-Step Solution: Classify each option: SO2, NO2, and dust are primarily emitted from sources (combustion, processes, fugitive dust).Photochemical smog results from VOC + NOx + sunlight, producing secondary oxidants.Therefore, the secondary pollutant among the options is photochemical smog. Verification / Alternative check: Air-quality textbooks consistently list ozone and photochemical oxidants as secondary, formed through chain reactions initiated by solar radiation. Why Other Options Are Wrong: Sulphur dioxide: directly emitted from combustion of sulfur-containing fuels. Nitrogen dioxide: primarily emitted directly or formed very near sources from NO oxidation; typically treated as primary for classification purposes. Dust particles: directly emitted (primary) from handling, roads, and grinding. Common Pitfalls: Confusing secondary smog with primary NO2; smog is a complex mixture dominated by secondary oxidants, especially ozone. Final Answer: Photochemical smog

Question 5

For a fabric (baghouse) filter, how does gas temperature (through its effect on density and viscosity) influence pressure drop across the bags and dust cake?

Accepted Answer

Introduction / Context: Bag filters capture particulates on a fabric medium. The pressure drop (ΔP) is a critical operating parameter influenced by filtration velocity, fabric and dust-cake resistance, and gas properties (notably viscosity and density), both of which vary with temperature. Given Data / Assumptions: Laminar/transition flow through porous media dominates pressure drop. Superficial gas velocity and dust-cake thickness are comparable across cases. Ideal-gas effects: density decreases as temperature rises at fixed pressure. Concept / Approach: For flow through porous media, ΔP often scales with gas viscosity and filtration velocity (Darcy-type behavior). Gas density influences dynamic terms and fan power; at a given mass flow, higher temperature lowers density, increasing volumetric flow and velocity, which in turn raises ΔP. Absolute static pressure itself does not linearly set ΔP across the filter—velocity/viscosity and cake resistance dominate. Step-by-Step Solution: Relate ΔP to gas properties: ΔP ∝ μ * v through fabric/cake resistance.Consider density indirectly via v: at constant mass flow, lower density → higher volumetric flow → higher v → higher ΔP.Therefore, ΔP increases with viscosity and (through velocity) density effects; option (b) captures this dependence best. Verification / Alternative check: Baghouse models and manufacturer curves show ΔP rising with temperature when viscosity increases and when volumetric flow rises due to density drop at constant mass flow. Why Other Options Are Wrong: (a) Inverse with viscosity is incorrect for porous-media flow. (c) Direct proportionality to absolute pressure is not the governing relationship for ΔP across the medium. Common Pitfalls: Ignoring the coupling between density, volumetric flow, and face velocity; neglecting cake conditioning and pulsing effects on resistance. Final Answer: Pressure drop is proportional to the viscosity and density of the gas.

Question 6

Occupational health: Workers chronically exposed to airborne mineral dusts in cement plants and limestone quarries are especially at risk of developing which disease?

Accepted Answer

Introduction / Context: Industrial hygiene in cement manufacturing and limestone quarrying focuses on controlling respirable dusts. Prolonged inhalation of crystalline silica can lead to fibrotic lung disease, making dust control and personal protection vital. Given Data / Assumptions: Work environment with silica-bearing mineral dusts (limestone, shale, raw meal, clinker). Chronic exposure without adequate respiratory protection. Focus on the most characteristic occupational disease. Concept / Approach: Silicosis is a progressive, irreversible pneumoconiosis resulting from inhalation of respirable crystalline silica (e.g., quartz). Cement and quarry environments generate fine particles during crushing, grinding, and handling. Silica exposure leads to lung fibrosis, reduced gas exchange, and increased susceptibility to tuberculosis. Step-by-Step Solution: Identify dust composition: raw materials and clinker contain silica.Relate exposure to disease: long-term silica inhalation → silicosis.Differentiate from other conditions: while asthma and general respiratory irritation can occur, the signature occupational hazard is silicosis. Verification / Alternative check: Epidemiological data and occupational standards (e.g., exposure limits for crystalline silica) underline silicosis as a primary risk in mineral-processing industries. Why Other Options Are Wrong: Cancer: not the typical direct outcome of silica dust exposure in these settings (though some risks exist depending on co-exposures). Asthma: possible irritant response, but not the hallmark chronic pneumoconiosis. Fluorosis: linked to fluoride exposure, not typical of cement/limestone dust. Common Pitfalls: Underestimating respirable fraction control; ignoring housekeeping, enclosure, and wet suppression; relying solely on disposable masks instead of comprehensive controls. Final Answer: silicosis

Question 7

Layers of the Earth’s atmosphere—identify the incorrect statement Which of the following statements about the troposphere, stratosphere, and mesosphere is WRONG for atmospheric science and environmental engineering practice?

Accepted Answer

Introduction / Context: Understanding the structure of the atmosphere is fundamental in environmental engineering, air-pollution control, and radio communication. Each layer—troposphere, stratosphere, mesosphere, thermosphere/ionosphere—has distinct properties that influence weather, ozone chemistry, and the propagation of electromagnetic waves. Given Data / Assumptions: Troposphere is the lowest layer, where most weather and clouds occur. Stratosphere lies above the troposphere and contains the ozone layer. Mesosphere lies above the stratosphere with low pressure and temperature. Long-distance high-frequency radio communication commonly relies on reflection/refraction by the ionosphere. Concept / Approach: The correct identification hinges on which layer reflects radio waves used in long-distance communication. It is not the stratosphere but the ionosphere (part of the thermosphere) that affects radio propagation. The other listed statements about troposphere dust/clouds and stratospheric ozone are standard facts in atmospheric science. Step-by-Step Solution: Recognize that the stratosphere sits above the troposphere and is ozone-rich—this is true.Note that the mesosphere has low temperature and pressure—also true.Recall that long-distance radio reflection occurs in the ionosphere, not the stratosphere.Therefore, the statement attributing radio wave reflection to the stratosphere is wrong. Verification / Alternative check: Radio engineering and atmospheric references consistently describe the ionosphere (approximately 60–1000 km altitude) as the region responsible for reflecting/refracting HF radio waves, enabling beyond-line-of-sight communication. Why Other Options Are Wrong: Option A: Correct—stratosphere with ozone layer shields UV radiation. Option B: Correct—mesosphere exhibits very low pressure and temperatures. Option C: Correct—troposphere contains most aerosols, clouds, and weather. Common Pitfalls: Confusing stratosphere with ionosphere because both are above the troposphere. Only the ionosphere significantly affects HF radio propagation. Final Answer: Long-distance radio waves are reflected back to Earth by the stratosphere.

Question 8

Air emissions from major industry—identify the common pollutant Which pollutant is commonly emitted from metallurgical smelters, thermal power plants, and cement plants, and is a key target for flue-gas desulfurization?

Accepted Answer

Introduction / Context: Sulfur dioxide is one of the most regulated air pollutants due to its role in acid rain formation, particulate sulfate generation, and adverse health impacts. Large stationary sources—especially coal-fired power plants, sulfide-ore smelters, and certain cement kilns—are classic emitters of SO2 unless equipped with control systems. Given Data / Assumptions: Fuel sulfur or sulfide minerals present in the feed contribute to SO2 during combustion/roasting. Smelters process sulfide ores (e.g., Cu, Ni, Pb), releasing SO2 during oxidation. Thermal power plants burning sulfur-bearing coal or oil emit SO2 without scrubbing. Cement plants can emit SO2 from fuel and raw-meal sulfur compounds. Concept / Approach: Link the sulfur-containing inputs to the formation of SO2 in high-temperature processes. Among the options, SO2 is the broadest common denominator across the three listed industries. NOx is also produced in combustion, but smelters’ defining pollutant is typically SO2 from sulfide oxidation. Mercury and fluorine emissions are more site-specific. Step-by-Step Solution: Identify sulfur sources in fuels/ores.Recognize oxidation at high temperature forms SO2.Confirm prevalence across smelters, power, and cement—select SO2. Verification / Alternative check: Emission inventories consistently rank SO2 as a primary pollutant from these sectors without abatement; FGD, sorbent injection, and low-sulfur fuels target SO2 reductions. Why Other Options Are Wrong: NOx: common in combustion but not a hallmark of sulfide-ore smelters like SO2. Hg: emitted mainly from certain coals; not universally high in smelters/cement. F: notable for some aluminum/cement processes, but not common to all three sectors. Common Pitfalls: Overgeneralizing NOx to all high-temperature processes; smelter emissions are characteristically sulfur-driven. Final Answer: Sulfur dioxide (SO2)

Question 9

Water treatment—what is the principal purpose of using chloramines? In a municipal or industrial water chemical treatment plant, the use of chloramines primarily ensures which outcome?

Accepted Answer

Introduction / Context: Chloramines (formed by combining chlorine with ammonia) are widely used in drinking-water treatment as an alternative or complement to free chlorine. They provide a persistent disinfectant residual in distribution systems and can reduce formation of regulated disinfection by-products compared to free chlorine alone. Given Data / Assumptions: Treated water already has solids and hardness largely controlled by standard processes. The goal is safe distribution over long networks with minimized by-products. Chloramines act primarily as secondary disinfectants. Concept / Approach: Disinfection is the primary mission of chloramination—especially maintaining a durable residual that survives long residence times. While chloramines can modestly influence taste/odour, they are not principally used for weed control or hardness removal; those require different unit processes (e.g., algaecides, lime-soda softening, ion exchange). Step-by-Step Solution: Identify chloramines’ key property: persistent disinfectant residual.Match to distribution system needs: long networks and biofilm control.Exclude hardness removal and reservoir weed control as unrelated functions.Select disinfection as the principal ensured outcome. Verification / Alternative check: Operational guidance from utilities emphasizes chloramination for residual maintenance and DBP control, validating disinfection as the primary purpose. Why Other Options Are Wrong: Taste & odour control: not the main reason, often managed by activated carbon or oxidation strategies. Weed control: involves reservoir management, algaecides, or mixing—chloramines are not used for this. Permanent hardness removal: requires softening; disinfectants do not remove hardness ions. Common Pitfalls: Assuming all chlorine-based chemicals remove hardness or solve taste issues; their primary role is microbiological safety. Final Answer: Disinfection (with a long-lasting residual)

Question 10

Particle size terminology in solids handling When a particulate specification states “80% passing 200-mesh (about 74 μm)”, the material is commonly termed as what?

Accepted Answer

Introduction / Context: In mineral processing, powder technology, and process engineering, size descriptors are linked to standardized sieves (mesh) or micrometre ranges. Correct terminology helps in specifying feeders, classifiers, filters, and dust-control equipment. Given Data / Assumptions: 200-mesh corresponds to about 74 micrometres opening. “80% passing” means the cumulative undersize is 80% at that cut. Application is in solids handling or milling specifications. Concept / Approach: Material that is largely finer than 200-mesh is routinely referred to as a “powder.” Terms like “grit” and “aggregate” align with coarser fractions (sand, gravel, stone). “Smoke” refers to very fine aerosols/combustion particulates in air, not bulk solids passing sieves. Step-by-Step Solution: Translate 200-mesh to ~74 μm.Note that 80% passing indicates fine bulk solids typical of powders.Eliminate terms for coarser materials (grit, aggregates) and airborne particulates (smoke).Select “Powder.” Verification / Alternative check: Industrial datasheets classify many milled products (cement, pigments, mineral fillers) as powders at similar or finer d50/d90 values, consistent with 80% passing 200-mesh. Why Other Options Are Wrong: Smoke: airborne combustion aerosol; not a bulk solid sieve designation. Grit: coarser, often millimetre-scale particles. Aggregates: coarse construction materials (sand to gravel), far larger than 74 μm. Common Pitfalls: Equating “dust” or “smoke” (airborne) with “powder” (bulk solid capable of being sieved). Final Answer: Powder

Question 11

Boiler water conditioning—role of trisodium phosphate (Na3PO4) In internal boiler water treatment, trisodium phosphate is primarily used to reduce which specific risk or problem?

Accepted Answer

Introduction / Context: Internal boiler water treatment aims to prevent scale, corrosion, and embrittlement by controlling alkalinity and precipitating hardness inside the boiler where it can be removed by blowdown. Trisodium phosphate (Na3PO4) is a cornerstone chemical in the phosphate treatment program. Given Data / Assumptions: Phosphate treatment substitutes strong caustic (NaOH) with phosphate to maintain alkalinity safely. Calcium reacts with phosphate to form non-adherent calcium phosphate sludge. Embrittlement is associated with very high local caustic concentrations at metal surfaces. Concept / Approach: Using Na3PO4 moderates alkalinity to the phosphate/pH window, minimizing the risk of caustic embrittlement and promoting scale-forming ions to precipitate as soft sludge. Oxygen removal requires chemical scavengers (e.g., sodium sulfite, carbohydrazide) or deaeration—functions distinct from phosphate chemistry. Step-by-Step Solution: Replace or limit NaOH by dosing Na3PO4 to maintain controlled alkalinity.Form calcium phosphate: Ca^2+ + PO4^3- → Ca3(PO4)2 (represented as precipitation within the boiler).Lower risk of intergranular cracking due to excessive local caustic—reducing caustic embrittlement.Confirm that turbidity, silica removal, and oxygen scavenging are separate treatments. Verification / Alternative check: Boiler treatment guidelines specify coordinated phosphate control or congruent phosphate control to both capture hardness and avoid free caustic conditions that cause embrittlement. Why Other Options Are Wrong: Turbidity: managed by clarification/filtration upstream, not by Na3PO4. Suspended silica: addressed via external softening or demineralization. Dissolved oxygen: removed by deaeration or oxygen scavengers, not phosphate. Common Pitfalls: Overdosing caustic and assuming high pH alone is beneficial; excessive free caustic promotes embrittlement and caustic gouging. Final Answer: Caustic embrittlement of boiler metal

Question 12

Removing iron and manganese from water—identify the ineffective method Which listed method alone cannot reliably remove dissolved iron and manganese from raw water to meet potable standards?

Accepted Answer

Introduction / Context: Groundwaters often contain ferrous iron (Fe^2+) and manganous manganese (Mn^2+). These cause staining, taste issues, and distribution problems. Treatment typically oxidizes dissolved species to insoluble oxides then removes them physically, or exchanges them on selective media. Given Data / Assumptions: Dissolved iron and manganese are initially in reduced soluble states. Final goal is compliance with drinking-water limits and aesthetic standards. Single-step chlorination is considered without filtration. Concept / Approach: Oxidation converts Fe^2+ to Fe(OH)3/Fe2O3 and Mn^2+ to MnO2 (often requiring higher pH or stronger oxidants). These particulates must then be removed by settling/filtration. Ion exchange or manganese-oxide coated media also remove these ions. Chlorination alone may oxidize but does not remove precipitated solids; without clarification/filtration, water remains non-compliant. Step-by-Step Solution: Recognize required sequence: oxidation → solids removal.Identify that ion exchange and specialized zeolite processes can remove Fe/Mn.Note that lime-soda softening co-precipitates Fe/Mn under proper pH.Conclude chlorination alone is insufficient for removal. Verification / Alternative check: Water treatment practice uses filters (e.g., greensand, MnO2 media) post-oxidation; residual particulates are not acceptable in finished water. Why Other Options Are Wrong: Ion exchange: effective with pretreatment to prevent fouling. Oxidation + filtration: standard and effective. Lime-soda or Mn zeolite: proven technologies for Fe/Mn control. Common Pitfalls: Assuming a disinfectant automatically removes metals; oxidation must be followed by solids capture. Final Answer: Chlorination (alone, without subsequent removal steps)

Question 13

Occupational health—pneumoconiosis and dust exposure “Pneumoconiosis” is a chronic lung disease caused by long-term inhalation of which type of industrial dust?

Accepted Answer

Introduction / Context: Pneumoconiosis refers to a family of occupational lung diseases resulting from prolonged inhalation of mineral and industrial dusts leading to lung fibrosis. In industrial hygiene, identifying the dust type guides prevention, monitoring, and regulatory control. Given Data / Assumptions: Exposure is chronic and at workplace levels. Classic examples: coal workers’ pneumoconiosis (anthracosis), silicosis, asbestosis, and siderosis. The question seeks a representative dust widely associated with the term. Concept / Approach: Among the listed choices, coal dust is historically and clinically the most recognized cause of pneumoconiosis (coal workers’ pneumoconiosis). Iron dust can cause siderosis (a milder pneumoconiosis), while uranium dust raises radiological hazards. Lime dust mainly causes irritation rather than classic fibrotic pneumoconiosis. Step-by-Step Solution: Recall common occupational diseases: coal dust → anthracosis.Compare alternatives: iron dust (siderosis), uranium (radiotoxic risks), lime (caustic irritation).Select coal dust as the prototypical agent for pneumoconiosis. Verification / Alternative check: Epidemiological data from mining regions confirm coal workers’ pneumoconiosis as a prevalent occupational lung disease over decades. Why Other Options Are Wrong: Uranium ore: radiological and heavy-metal toxicity dominate, not classic pneumoconiosis prevalence. Iron ore: associated with siderosis but less fibrogenic than coal/silica. Lime dust: irritant and caustic, not primarily fibrogenic. Common Pitfalls: Assuming any dust equals pneumoconiosis; fibrogenicity and particle characteristics matter. Final Answer: Coal dust

Question 14

Groundwater chemistry—common forms of iron and manganese In reduced groundwater conditions, iron and manganese pollutants are most commonly present in the soluble form of their __________.

Accepted Answer

Introduction / Context: Groundwaters drawn from anoxic aquifers often contain dissolved iron and manganese. Knowledge of their chemical speciation informs the design of aeration, oxidation, and filtration steps in water treatment plants. Given Data / Assumptions: Reduced conditions (low dissolved oxygen) prevail underground. pH is near neutral to slightly alkaline, with dissolved carbon dioxide present. Dominant soluble species for Fe and Mn are required. Concept / Approach: Under anoxic, carbon dioxide–bearing conditions, Fe^2+ and Mn^2+ tend to exist as soluble bicarbonate complexes (e.g., “ferrous bicarbonate,” often represented as Fe(HCO3)2 in water chemistry shorthand). Upon aeration/oxidation, these convert to insoluble oxides/hydroxides that can be filtered. Step-by-Step Solution: Recognize groundwater dissolution of carbonate minerals yields bicarbonate alkalinity.Note that ferrous and manganous ions form soluble bicarbonate species.Select bicarbonates as the commonest dissolved forms in reduced groundwater. Verification / Alternative check: Standard texts depict Fe^2+ and Mn^2+ stability fields showing solubility in reducing conditions and precipitation after oxidation to Fe(OH)3 and MnO2. Why Other Options Are Wrong: Carbonates: typically sparingly soluble at neutral pH; metals tend to remain as bicarbonates in CO2-rich waters. Chlorides: may be present but are not the prevalent complexing form for Fe/Mn in natural groundwater. Sulfides: occur in strongly reducing, sulfidic environments, not the most common case. Common Pitfalls: Confusing solid carbonate minerals with aqueous bicarbonate species; the aqueous form dominates under typical aquifer conditions. Final Answer: Bicarbonates

Question 15

Community noise—jet engine with afterburner Approximately what sound pressure level (SPL) in decibels is measured about 100 metres from a jet engine operating with afterburner?

Accepted Answer

Introduction / Context: Environmental noise assessment requires order-of-magnitude understanding of typical sources. Jet engines, especially with afterburners engaged, are among the loudest continuous man-made sources encountered near airports and testing facilities. Given Data / Assumptions: Distance from source: about 100 m in free field conditions. Source: jet engine with afterburner (very high thrust and exhaust velocity). Reference is A-weighted or overall SPL estimates for practical comparisons. Concept / Approach: Typical SPL values decay with distance approximately according to spherical spreading and atmospheric absorption, but the levels remain extremely high close to the source. Around 100 m, SPLs near 140 dB are reported for afterburning engines, which is near the threshold of pain and requires stringent hearing protection and exclusion zones. Step-by-Step Solution: Recall benchmark SPLs: 120 dB (threshold of discomfort), ~140 dB (near pain), >160 dB uncommon outside blast events.Cross-reference typical jet engine measurements at 100 m with afterburner engaged.Select 140 dB as the representative value.Reject implausible extremes (170–200 dB) for this distance in standard conditions. Verification / Alternative check: Noise control literature lists 130–150 dB ranges near military afterburning jets at tens to hundreds of metres, making 140 dB a reasonable central figure. Why Other Options Are Wrong: 120 dB: too low for afterburners at 100 m. 170 or 200 dB: levels typical of explosions/shock fronts at much closer ranges, not sustained engine operation at 100 m. Common Pitfalls: Ignoring logarithmic decibel scaling; small numeric differences represent large intensity changes. Final Answer: 140 dB

Question 16

Drinking-water safety—mercury threshold limit value (TLV) The approximate permissible concentration (TLV) of mercury in potable water is closest to which value (ppm)?

Accepted Answer

Introduction / Context: Mercury is a potent neurotoxin with strict regulatory limits in drinking water. Process engineers working on water treatment and environmental compliance must know typical threshold values to design appropriate removal systems and monitoring programs. Given Data / Assumptions: Units are parts per million (ppm), where 1 ppm = 1 mg/L. Question seeks an order-of-magnitude TLV appropriate for safe potable water. Conservative health-based guidelines target very low concentrations. Concept / Approach: Public health guidelines set mercury limits in the microgram per litre (μg/L) range. A value of 0.001 ppm equals 1 μg/L, which aligns with stringent international standards depending on the mercury species and jurisdiction. Higher options (0.1–5 ppm) are orders of magnitude too high for potable water. Step-by-Step Solution: Convert options to μg/L: 0.001 ppm = 1 μg/L; 0.1 ppm = 100 μg/L; 1 ppm = 1000 μg/L; 5 ppm = 5000 μg/L.Compare with typical regulatory limits in the low μg/L range.Select 0.001 ppm as the closest safe threshold magnitude.Reject larger values that exceed health-protective standards by 100× to 5000×. Verification / Alternative check: Many jurisdictions specify mercury limits at or near 1–2 μg/L for total mercury in drinking water, consistent with 0.001–0.002 ppm guidance levels. Why Other Options Are Wrong: 0.1, 1, 5 ppm: far above accepted health-based limits; such levels would trigger immediate advisories. Common Pitfalls: Confusing ppm with ppb; remember that 0.001 ppm equals 1 ppb (μg/L), which is within the accepted safe range. Final Answer: 0.001 ppm

Question 17

Combustion troubleshooting: In industrial furnaces and boilers, visible smoke formation is primarily caused by which combination of factors?

Accepted Answer

Introduction / Context: Visible smoke from a furnace, kiln, or boiler stack is a classic sign of incomplete combustion. For plant engineers and operators, recognizing the common root causes helps reduce fuel waste, meet emissions norms, and protect heat-transfer surfaces from soot deposition. Given Data / Assumptions: The system burns gaseous, liquid, or pulverized solid fuels. Smoke is defined as visible particulate (soot, unburned carbon, tarry aerosols). Normal objectives: complete combustion, minimal unburned hydrocarbons, and acceptable excess-air levels. Concept / Approach: Smoke appears when fuel carbon or heavy hydrocarbons are not fully oxidized to CO2 and H2O. This typically occurs when any of three conditions prevail: not enough oxygen (air deficiency), inadequate time or temperature for reactions to finish, or poor mixing between fuel and air. Equipment design and operating load strongly influence these factors. Step-by-Step Solution: 1) Air deficiency: Too little excess air limits oxygen, causing partial oxidation and soot formation.2) Inadequate time/temperature: Short residence time or low flame temperature prevents burnout of soot nuclei.3) Poor mixing: Maldistributed air or poor atomization leaves fuel-rich pockets where pyrolysis generates smoke.4) Equipment/operation: Undersized burners, fouled tips, overloading, and flawed furnace aerodynamics worsen mixing and residence time.5) Fuel quality: High-asphaltene oils, contaminated or variable fuels increase smoke propensity without proper atomization and preheat. Verification / Alternative check: Stack opacity and flue-gas analysis (O2, CO, unburned hydrocarbons) confirm incomplete combustion. Corrective actions include optimizing excess air, improving atomization, tuning burner registers, restoring design heat input rates, and ensuring proper draft balance. Why Other Options Are Wrong: (a) Alone: Design/overloading is only one piece; smoke also depends on mixing and air.(b) Alone: Air/time issues matter, but fuel and mixing quality also critical.(c) Alone: Poor fuel or mixing is insufficient explanation by itself. Common Pitfalls: Overcorrecting with excessive excess air, which increases NOx and stack losses.Ignoring burner maintenance and atomizer health. Final Answer: All of the above (a), (b), and (c)

Question 18

Air emissions profile: Which set lists the most common primary pollutants released by the iron and steel industry?

Accepted Answer

Introduction / Context: Integrated iron and steel plants emit a characteristic set of pollutants from sinter plants, coke ovens, blast furnaces, basic oxygen furnaces, and reheating furnaces. Knowing the typical pollutants helps target control technologies and comply with environmental regulations. Given Data / Assumptions: Typical fuels: coke oven gas, blast furnace gas, natural gas, and auxiliary liquid fuels. High-temperature thermal processes with combustion and reduction reactions. Focus on primary gaseous pollutants, not particulate or metals. Concept / Approach: Carbon monoxide (CO) and carbon dioxide (CO2) arise from combustion and reduction reactions (CO as a reductant in blast furnaces). Sulfur dioxide (SO2) primarily originates from sulfur in coke and heavy fuels. While nitrogen oxides (NOx) may also be present, the question asks for the main pollutants traditionally associated with the sector, prominently CO/CO2/SO2. Step-by-Step Solution: 1) Evaluate CO: Produced in large quantity in BFs and combustion systems; significant pollutant and energy carrier.2) Evaluate CO2: Unavoidable product of oxidation and calcination; major greenhouse gas.3) Evaluate SO2: Formed when sulfur in fuels/coke oxidizes.4) Compare options: Sets containing H2S or NO as primary are less characteristic for bulk emissions from steelworks; SO3 and NO2 are secondary or smaller fractions relative to SO2 and overall NOx. Verification / Alternative check: Emission inventories for steel plants consistently highlight CO, CO2, SO2 (along with NOx and particulates) as principal pollutants requiring control (e.g., desulfurization, optimized combustion, scrubbers, ESP/baghouse for dust). Why Other Options Are Wrong: H2S, NO, SO3: H2S emissions are more typical of sour gas processing; SO3 is a minor fraction formed downstream.CO2, H2S, NO2: H2S/NO2 are not the dominant trio for steel emissions.SO3, NO2, CO2: SO3 and NO2 are less predominant than SO2 and mixed NOx. Common Pitfalls: Confusing primary pollutants with secondary ones formed in the atmosphere.Overlooking CO as both pollutant and energy resource in steel plants. Final Answer: CO, CO2 and SO2

Question 19

Particulate control: Which device is the least efficient for capturing submicron (< 1 μm) particles in industrial dust collection?

Accepted Answer

Introduction / Context: Industrial processes generate a wide particle-size spectrum. Submicron particles are particularly challenging to capture due to their low inertia and high diffusivity. Choosing an appropriate control device depends on the collection mechanism (inertial impaction, interception, diffusion, electrostatic attraction, and filtration). Given Data / Assumptions: Target: submicron particles (< 1 μm). Devices compared: cyclone, gravity chamber (dust catcher), bag filter, wet scrubber. Goal: identify the least efficient among the listed for this size range. Concept / Approach: Gravity settling chambers remove large, high-inertia particles primarily via gravitational settling. Their cut size is typically hundreds of microns, making them ineffective for fine aerosols. Cyclones improve on gravity by using centrifugal forces, but still struggle below ~3–5 μm unless specially designed. Bag filters and high-energy scrubbers offer significantly better fine-particle capture. Step-by-Step Solution: 1) Gravity dust catcher: Minimal residence time and low driving force → very poor for submicron particles.2) Cyclone: Better than gravity for 5–10 μm and above, still weak for submicron.3) Bag filter: Surface/depth filtration captures submicron by diffusion and interception; high efficiency.4) Wet scrubber: High-energy types (venturi) can collect submicron via impaction on droplets.5) Therefore, the least efficient is the gravity dust catcher. Verification / Alternative check: Device performance curves show precipitous drop in efficiency below a few microns for gravity and standard cyclones, while fabric filters and venturi scrubbers maintain high capture rates. Why Other Options Are Wrong: Cyclone separator: Inefficient for submicron but still superior to a gravity chamber.Bag filter: Designed to capture fine particles with very high efficiency.Wet scrubber: High-energy designs achieve notable submicron removal. Common Pitfalls: Assuming all dust devices perform similarly regardless of particle size.Overlooking filtration and diffusion mechanisms crucial at small sizes. Final Answer: Dust catcher (gravity settling chamber)

Question 20

Occupational health: Siderosis is a pneumoconiosis primarily caused by inhalation of which type of dust?

Accepted Answer

Introduction / Context: Pneumoconioses are lung diseases caused by chronic inhalation of mineral or metal dusts. In heavy industry, welding, foundries, and ore handling create specific exposure profiles. Correct identification supports proper PPE, ventilation, and regulatory compliance. Given Data / Assumptions: Workers may be exposed to iron, silica, or coal dusts. Question asks specifically about siderosis. Focus on the etiologic agent (dust type), not clinical management. Concept / Approach: Siderosis (from Greek “sideros,” iron) is an iron-oxide dust deposition disease. Radiographically, it may show characteristic opacities without the fibrosis degree associated with silicosis. Exposure arises from welding fumes, grinding, and iron ore handling. Step-by-Step Solution: 1) Match disease to dust: siderosis ↔ iron/iron-oxide dust.2) Differentiate from silicosis (silica) and coal workers’ pneumoconiosis (coal dust).3) Select the correct dust: iron. Verification / Alternative check: Occupational hygiene literature consistently associates siderosis with iron oxide inhalation, especially in welders and metal grinders. Why Other Options Are Wrong: Silica dust: Causes silicosis, a different disease with notable fibrosis.Coal dust: Causes coal workers’ pneumoconiosis (anthracosis), not siderosis.None: Incorrect because siderosis has a known causative dust (iron). Common Pitfalls: Confusing the various pneumoconioses due to overlapping industrial environments.Assuming all dust-related lung diseases have identical pathology. Final Answer: Iron dust

Environmental Engineering Questions