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Question 18 PDF Print E-mail

Q18 What effects, if any, is there on an inactive storage pile of PRB coal in terms of weight, btu etc over

a period of time. The pile has been compacted and chemically treated for erosion.

 

A18 The catch there is the word inactive. The stockpile inventory folks do borings and quality samples,

but shouldn’t be able to provide the data w/o the client’s permission. If the clients would like to participate

then the data could be reviewed. An inactive pile that has been assessed for quality more than once

would be a rarity. Espcially on PRB, which disappears quickly in todays market. Still, PRB coal is extremely

friable and will break down into smaller particles, virtually independent of how the coal is transported or

handled.

 

PRB represents the extremes of handling problems: dust is an issue when the coal is fine and dry.

Bunker and chute plugging is an issue when the same fine coal is wet. Once the coal is exposed by mining,

the degradation process begins – the majority of the damage can occur in a very short time, even as short

as a few days. The extent of the degradation that occurs depends in large part on the distance to the plant

from the mine, i.e., how long the coal is exposed to the atmosphere during transportation. Additional factors

such as crushed run of mine (CROM) size, and specific handling procedures also impact the degradation

process. Additional decomposition occurs during handling and storage in a pile and bunker, bin or silo.

 

The following citation summarizes it well. "We believe that the root cause of the degradation is loss of moisture that impacts the coal both

mechanically and through the generation of additional surface reaction area, chemically. The combination

of the two is what makes PRB coal so difficult to handle."  Hossfeld and Hatt, "PRB Coal Degradation –

Causes and Cures", www.coalcombustion.com/.../PRB%20Coal%20Degradation.doc

 

This is a good citation because it shows the fragile nature of the Sub bituminous C coal, and should be

enough to satisfy the question without going into the specifics of individual stockpiles.

 

Here is a second citation that is often quoted. "There is a loss of heating value for coal stored for long

periods as they tend to react with oxygen in the air, a process called weathering. The rate is normally

around 1% in the first year of storage, but may be as high as 3% for low rank coals (Skorupska, 1993).

 

 
Question 17 PDF Print E-mail

Q17:  Where in HB44 does it state that you must material test a belt-conveyor scale annually?

A17: 

A short answer is “It is not posted in HB44”.  It is a common practice however for most States to require a material test annually.  We suggest you contact the person with statutory authority in your area as to how often they require a material test.

 

An explanation as to why they don’t post a time for material testing in HB44 was offered by John Barton, National Institute of Standards and Technology (NIST)

 HB44 does not contain any references to the frequency required for an official test on belt-conveyor scales or any other device for that matter.  The state and local weights and measure programs are responsible for the enforcement of the requirements contained in HB44.  To require that the content of the HB44 Codes be enforced at regularly established intervals would be dictating priorities and the best use of the resources available to those regulatory agencies. Today most of these weights and measures programs are operating with very limited resources and personnel and must make use of what is available as the administrators see fit.  It would be unreasonable to expect these weights and measures programs to devote what resources are available to areas of responsibility in a uniform and concerted fashion.  Various aspects that are unique to different jurisdictions have a strong influence on the amount of effort and time concentrate on individual areas of weights and measures concerns.  For instance, a large industrial metropolitan area will not expend a large amount of weights and measures resources on devices that are typically found in more rural or suburban areas (farm, milk tanks, livestock scales, etc. The absence of this type of requirement allows for more flexibility within the many different enforcement agencies in the U.S. and permits them to get the most from what is available within their programs.  
 
Question 16 PDF Print E-mail

Q16:  During a discussion with a client,  the question came up as to why are sampling manufacturers changing from the standard three roll idlers under the sweep sampler to multiple rolls, when all the manufacturers have said bias tests have proved no bias with the three roll idlers.  I understand one of the reasons was they are trying to get all the material in the corners, but again the three rolls didn't show bias in the past, so why change?

 
Question 15 PDF Print E-mail
Q15:  Is a Coupled in Motion (CIM) double draft track scale, if used with cars un-coupled, an acceptable reference scale used to material test a belt-conveyor scale? Over the years double draft track scales have been used successfully for material testing belt-conveyor scales.  The State said no, and I was surprised because I have used the CIM double draft in other States with no problems.

A15:  Coupled In Motion (CIM) Railway Track Scales have been used as a reference scale by many States, however, their use requires the rail cars to be un-coupled and double draft weighed. The CIM scale must be tested and verified to weigh to an accuracy of +/- 0.1 percent statically prior to material testing the belt-conveyor scale. Not all States will allow the double draft testing in this manor so we suggest you check with the local person with statutory authority prior to going forward with a double draft weighing reference scale.

 
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