1. Sentry Equipment Corporation
Process Sampling
Sentry Equipment Corporation

2. Objective
Gain an understanding of the methods to obtain representative samples
Review the fundamentals of gases, liquids and bulk solids
Overview of analyzing methods
Review the integration of sampling with on-line instrumentation

3. Why do we sample? Product mix characteristics
Examples: Particle size, bacteria count, chemistry, etc.
Identify process variations
Process control
Environmental monitoring
Product quality assurance
Custody transfer

4. What kind of sample?
“True” overall average of the entire lot for one or many characteristics
Representative sample
Characteristics of the sample equal that of the entire lot or batch
Consistent, accurate, and repeatable

5. How to get a representative sample
Follow protocol that gets a consistent, accurate, and repeatable sample
Understand the material physical properties
Use techniques that have as little sample bias as possible
Profile the process and sampling system (i.e.. Liquids, slurries, gases, bulk solids, etc.)
Reduce sample to sample variation
Sample methods and results must be repeatable

6. Sampling Errors
Process analysis is only as good as the quality and representivity of the sample itself
Sampling errors are costly because they can lead to:
Unnecessary process changes
Additional analysis of more samples
Release of off-spec product to the customers
Scrap of good material
The Sampling Scapegoat

7. General Sampling Practices
Understand the process and the sampling objective to help select the proper device
I.e. Gas concentration, liquid chemistry, bulk solids particle size analysis
Determine the best sampler location
Take several increments and composite them to form the “sample”
Composite Sample – A sample obtained by combining several distinct sub-samples or increments
Sample frequently enough to identify process cycles

8. Direct Sampling
Typically includes dipping a cup or container into an open vessel or opening a spigot on a vessel that may be under pressure
May require the process to be interrupted in order to sample
This sampling technique is generally considered unsafe
Operator is exposed to any process or environmental hazards
Direct sampling introduces the ability for sample variations due to human error and sample contamination

9. Indirect Sampling
Indirect sampling isolates the operator from the process hazards
Maintains a closed system
Sample integrity preserved
Allows the process to be sampled during normal production cycle

10. A few general sampling practices
Mix the material prior to sampling (if possible)
Take several increments and composite them to form the “sample”
Composite Sample – A sample obtained by combining several distinct sub samples or increments
Collect the sample in a container that will not react with the sample
Sample frequently enough to identify process cycles

11. A few general sampling practices (cont.)
Determine the correct size required for the sample
Use a sampler and sampling process that removes bias
Understand the process
Sampling practices may vary from process to process

12. Three categories for sampling variation
Process variations/cycles
Material variation
Tool and techniques
Including sample handling

13. Process Variations
Be aware that the process and its conditions may vary over time
Examine the sampling results and the effects of sampling frequency
Use the sampler and sampling system to verify the process

14. Ways to reduce material variation
Determine the appropriate mass of the actual sample
Provides a better idea about the overall properties of the lot
Collect several increments from the lot and form a composite sample
Condition the material prior to sampling
Mix the sample if possible
Control the temperature, pressure, flow, etc.
Control the particle size

15. Product Characteristics
Identification of the product characteristics is critical for obtaining a representative sample
Every gas, liquid, and bulk solid has its own unique physical property
Many processes contain entrained gases that can expand when decompressed
Venting provisions must be taken into account
Bulk solid characteristics can be very unpredictable
Some may pack one moment and fluidize the next
Two grades of the same material may act differently

16. Flow Characteristics Mass Flow Funnel Flow Arching/Bridging Rat-holing
Flooding
Segregation
Improper bin design affects the flow of solids in the bin or hopper.

17. Material Properties
Abrasive – Materials that wear, grind, or rub on the inside of the sampler or any moving part
Arching/Bridging – Materials that tend to form a bridge-like structure
Free-Flowing – Materials that generally flow under the influence of gravity without the aid of agitation
Floodable – Materials that aerate to a point where they begin to flow like a liquid
Hygroscopic – Materials that tend to absorb and retain moisture from the atmosphere

18. Material Properties Cohesive – Materials that tend to stick to itself
Adhesive – Materials that tend to adhere or stick to components of the sampler
Friable – Materials that are easily pulverized or broken apart
Static Generating – Materials that generate static from friction on itself or within the sampler

19. Bulk Density
Mass per unit of volume in powder form, including the air trapped between the particles
Measured in g/cc, kg/l, lb/ft3
Examples:
Cake Mix = 44 lb/ft3 (0.705 g/cc)
Cement Powder = 85 lb/ft3 (1.361 g/cc)
Oats = 27 lb/ft3 (0.432 g/cc)
Parsley Flakes = 3 lb/ft3 (0.048 g/cc)
Sand = 99 lb/ft3 (1.586 g/cc)
Tungsten Carbide = 250 lb/ft3 (4.004 g/cc)

20. Tools and Techniques

21. Sampling Tool
The sampling tool is critical for providing a representative sample
The sampler must assure the sample integrity is preserved
Understand the analysis requirements to help determine which sampler to choose
Understand the process variables that may impact the sampler design
The sampler should keep the operator safe from any process or environmental hazards

22. Principle for correct sampling
Every part of the lot has an equal chance of being in the sample
Integrity of the sample is preserved before, during, and after sampling
Oxidation, abrasion, evaporation, and contamination are examples of improper handling
Vapor pressure is an important characteristic to take into account when sampling
The measure of the tendency of a material to form a vapor.

23. Manual “Grab” Samples
Typically, manual grab sampling is a poor, but common practice because it is taken from the most accessible part of the batch/process
Exception is when the sampler is located in a proper/acceptable sample point and other good practices are recognized

24. Gas Sampling Maintain pressure and sample integrity
Monitor H2S, VOCs, water content
Speed loops and analyzers are common

25. Liquid Sampling Control pressure, temperature, flow rate
Monitor pH, DO, Sodium, conductivity, TOCs, chemistry, etc.
On-line analysis is common

26. Bulk Solids Sampling Material characteristics and flow properties vary
Monitor moisture, particle size, shape, etc
Difficult to analyze on-line
Material waste

27. Bulk Solids Sampling
Point Sample
Strip Sample
Cross Cut Sample

28. Point Samplers Takes a sample from a point in the material stream
Used when conducting chemical analysis or when material is homogenous

29. Strip Samplers Takes a sample from a narrow portion of the stream
Used in situations where product segregation exists

30. Cross Cut Samplers Takes a cross-section of the entire product stream
Provides the most representative sample, but requires a lot of headroom

31. Types of Measurements and Technology

32. Frequent Sample analysis conducted in real time
Off, At and On-Line
Off-Line
At-Line 
Sample removed and tested locally
On-Line 
Frequent Sample analysis conducted in real time
Lab Testing
Infrequent Samples sent to a remote location 

33. Measurements/Analysis
Effusivity
NIR IR
Laser Induced Fluorescence
Light Scattering
Imaging
Particle Size
Moisture
Chemical Composition
Surface Area
Shape
Temperature
Dissolved Oxygen

34. Knowledge
What you
know
don’t know
What you don’t know
that you don’t know
Monitoring multiple properties provides insights into areas and mechanisms that have not been investigated

35. Summary
Sampling is a critical part of process control and is often overlooked
Indirect methods of sampling are the safest, yet most challenging
The goal is to get representative samples
Material and process variations as well as sampling techniques and tools effect our ability to get representative samples
Understand the process and sampling objectives
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