Question 3 of 7: Measurement Techniques and Particulate Characteristics

Question 3: Measurement Techniques and Particulate Characteristics (20 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

(i) Cement Kiln Emissions and the Role of Particle Size

A long rotary kiln firing high-sulphur, high-vanadium petroleum coke around the clock is a classic cement/lime kiln configuration. Alongside CO₂ and water vapour, the expected emissions are: particulate matter dominated by fine cement kiln dust (CKD) — a large fraction of it condensable, sub-micron alkali (K, Na) chloride/sulphate fume that volatilizes in the hot burning zone and recondenses in the cooler gas stream — plus SO_x (petroleum coke is characteristically high in sulphur), NO_x (from the high flame temperature), and CO from any locally incomplete combustion. A large baghouse together with an electrostatic precipitator (ESP) are used specifically to control this particulate matter — the fine CKD/alkali fume and the coarser process/raw-meal dust entrained in the kiln gas stream.

Particle size distribution is central to both the environmental fate and the choice of control technology. The finest particles (sub-micron condensable fume and the PM_2.5 fraction) penetrate deepest into the respiratory tract, scatter light most efficiently (dominating visibility/haze impact), and settle so slowly that they travel the farthest downwind before deposition — they therefore drive both the health-risk and the regional-transport concerns, and require a high-efficiency polishing device (a baghouse's fine-fibre filtration, or an ESP sized with adequate specific collection area) rather than a simple gravitational or cyclone pre-collector, which only removes the coarse fraction economically. Coarse process dust, by contrast, settles out quickly near the source and can be captured cheaply upstream, reducing the fine-particle control device's loading.

(ii) In-Stack Measurement Techniques

Isokinetic manual sampling (EPA Method 5). A probe withdraws a gas sample from the stack at the same velocity as the local stack gas (isokinetic sampling, avoiding size-biased sub- or over-sampling of particulate), passing it through a heated filter; the collected particulate mass, divided by the sampled gas volume, gives a directly traceable PM concentration — the reference method against which continuous monitors are calibrated.

Continuous emissions monitoring systems (CEMS). Extractive or in-situ analyzers (UV/IR/NDIR gas analyzers for SO₂, NO_x, CO; opacity/transmissometers as a continuous PM surrogate) report concentrations in near-real time, allowing compliance demonstration and process control every operating hour rather than only during periodic stack tests.

(iii) PM_2.5 vs. PM₁₀

(1) Health effects. PM_2.5 (fine particulate, ≤2.5 µm) penetrates past the upper airway defences into the alveolar region and can cross into the bloodstream, and is strongly associated with cardiovascular disease and premature mortality; the coarse fraction that makes up the rest of PM₁₀ (2.5–10 µm) deposits mainly in the upper respiratory tract and larger bronchi, producing more localized irritation and asthma triggering with less systemic effect.

(2) Aesthetics. PM_2.5 (including secondary sulfate, nitrate and organic aerosol) is the dominant contributor to visibility degradation and regional haze, because particle diameters near the wavelength of visible light scatter it most efficiently, and fine particles stay airborne and travel long distances; the coarse PM₁₀ fraction (mechanically generated dust, pollen) settles out much faster and contributes more to localized soiling and nuisance dust near the source than to regional haze.