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ASME PTC 28-1965 (1979) scan — Determining the Properties of Fine Particulate Matter
📐 ASME PTC 28-1965 (reaffirmed 1979) is the ASME Performance Test Code for determining the physical and chemical properties of dust, serving the design and evaluation of dust separating apparatus. Recognition of the need for standardized methods and measuring equipment to determine the size of small particulate matter in dust and smoke led, in November 1954, a group of engineers from leading utilities and equipment manufacturers to recommend that the ASME Power Test Codes Committee prepare such a code. PTC Committee No. 28 on the Measurement of Small Particulate Matter was organized in April 1955, made maximum use of the work of ASTM and the Air Pollution Control Association, and received cooperation from the U.S. Public Health Service, whose Robert A. Taft Sanitary Engineering Center performed research to develop “standard samples” of sub-sieve-size material for calibrating the instruments used for terminal-velocity distribution determination. The code was approved in April 1964 and published in July 1965.
💡 Before sizing a dust collector you must answer three questions: how big are the particles, how conductive are they, and how moist/combustible are they? PTC 28 quantifies these properties with a standard set of methods — the base data for selecting electrostatic precipitators, baghouses, and cyclones.
1. Object and Scope 📌
The object of the test is to determine various physical and chemical properties of dust and to define the terminology used in stating those properties. The limitations of scope:
- Definition of dust: gas-borne solid particles having terminal velocities greater than 0.1 inch per minute in air; the larger gas-borne particles (terminal velocities above 1000 inches per minute) from combustion of solid fuel are usually called “cinders” but fall under the general heading of dust.
- Distinction from smoke: smoke results from incomplete or arrested combustion of the volatile constituents of fuels and usually consists of particles with terminal velocities less than 0.1 inch per minute; soot is composed of agglomerated smoke particles.
- Sampling is outside this code: samples of gas-borne dust taken from a duct are assumed taken in accordance with the Test Code for Determining Dust Concentration in a Gas Stream (PTC 27-1957); sampling from a large bulk in a hopper or silo is not recommended, and if necessary the methods must be defined in a written agreement of all parties to the test.
- Precedence: where directions in this code for a particular measurement differ from those in other ASME Power Test Codes for similar measurements, this code prevails unless otherwise agreed.
⚠️ Sample representativeness is the soul of dust testing: an unrepresentative sample invalidates every subsequent property determination. Always follow the isokinetic sampling principle of PTC 27 when collecting from a gas stream, and avoid hopper and silo locations prone to segregation.
2. Properties Determined 🔧
| Property | Essentials of the method | Engineering significance |
|---|---|---|
| Terminal velocity distribution | Centrifugal classifier (Appendix 5.02–5.10), calibrated with standard samples | Base distribution curve for gravity/inertial separator design |
| Specific gravity | Ratio of true particle volume weight to that of pure water at 4 °C (excluding interparticle voids) | Volumetric flow and settling calculations |
| Sieve analysis | U.S. Standard Sieve Series; weight-percent size distribution | Conventional characterization of coarser fractions |
| Bulk electrical resistivity | Resistance of a 1-cm cube of sample at 90% of breakdown voltage (Ω·cm) | Key parameter for electrostatic precipitator (ESP) efficiency |
| Moisture content | Drying loss under prescribed conditions | Affects adhesion, conductivity, and corrosion |
| Loss on ignition | Weight loss on ignition at specified temperature | Combustible content — relates to explosion and re-ignition risk |
| Water-soluble content and sulfate | Water extraction followed by determination | Corrosivity assessment and dust cementation |
| Bulk density | Weight per unit volume of freely settled material under prescribed conditions | Hopper sizing, conveying, and ash removal design |
| Specific surface | Surface area per unit weight by the prescribed method | Fine-particle agglomeration, adsorption, and chemical reactivity |
3. Test Methods, Calibration, and Standard Samples 📏
- Terminal velocity distribution: terminal velocity is the equilibrium velocity, in inches per minute, with which a particle freely falling through dry air at 68 °F and 29.92 in Hg abs reaches when drag equals gravity. The distribution is presented as a table or graph of percent by weight of particles having terminal velocities less than various stated values.
- Centrifugal classifier: installation, operation, and calibration are given in Appendix 5.11; classifier results are converted via the terminal-velocity-versus-particle-diameter relationships of Appendix 5.13–5.15.
- Standard samples: standard samples of sub-sieve-size material, prepared with the cooperation of USPHS, are used to calibrate instruments for terminal-velocity distribution (Appendix 5.12), ensuring inter-laboratory comparability.
- Reporting: the test conditions (equilibrium state, temperature, etc.) and all terminology used must be fully stated in the report.
💡 Electrical resistivity is the “barometer” of ESP sizing: below ~10⁴ Ω·cm particles lose charge and are re-entrained; above ~10¹¹ Ω·cm back corona develops — both collapse collection efficiency. Conditioning (water injection, ammonia) is commonly applied on site to improve resistivity.
4. Engineering Practice Essentials 🛠️
- Collector selection: gravity and inertial separators are designed on the terminal velocity distribution; baghouses focus on size, moisture, and specific surface; ESPs require resistivity and size distribution.
- Inter-lab checks with standard samples: use the same calibration samples for comparisons so terminal-velocity-distribution data remain comparable across organizations.
- Sampling + testing in series: first sample per PTC 27 for concentration, then measure properties per PTC 28 — together they form the complete flue-gas dust evaluation chain.
- Result corrections: state the equilibrium conditions (e.g., air-equilibrated environment) in the report and correct to the standard reference when necessary.
5. Frequently Asked Questions ❓
❓ Q: How are dust and smoke distinguished?
A: By the 0.1 in/min terminal-velocity boundary: above it, dust (e.g., fly ash particles); below it, smoke (products of incomplete combustion); soot is agglomerated smoke particles.
A: By the 0.1 in/min terminal-velocity boundary: above it, dust (e.g., fly ash particles); below it, smoke (products of incomplete combustion); soot is agglomerated smoke particles.
❓ Q: Why measure bulk electrical resistivity?
A: ESP collection efficiency depends strongly on resistivity: too low, particles lose charge and are re-entrained; too high, back corona (even breakdown) forms in the ash layer — both sharply reduce efficiency.
A: ESP collection efficiency depends strongly on resistivity: too low, particles lose charge and are re-entrained; too high, back corona (even breakdown) forms in the ash layer — both sharply reduce efficiency.
❓ Q: What is the role of standard samples?
A: They calibrate the centrifugal classifiers and other instruments used for terminal-velocity distribution, making data from different laboratories and batches comparable — the key to a meaningful “terminal velocity distribution.”
A: They calibrate the centrifugal classifiers and other instruments used for terminal-velocity distribution, making data from different laboratories and batches comparable — the key to a meaningful “terminal velocity distribution.”
🔍 Q: What is the relationship between this code and PTC 27?
A: PTC 27 determines dust concentration in a gas stream (how much ash and how to sample); PTC 28 determines dust properties (what the ash is like); together they form the complete dust evaluation workflow.
A: PTC 27 determines dust concentration in a gas stream (how much ash and how to sample); PTC 28 determines dust properties (what the ash is like); together they form the complete dust evaluation workflow.
