Reducing Derates with Real-Time Control of Coal Quality Using PGNA On-line Elemental Analyzers at Choctaw Generation Red Hills Power in Northeast Mississippi

Steve Foster Executive Vice President; SABIA, Inc.

Bob Halsell Technical Coordinator; North American Coal Red Hills Mine

Abstract

The North American Coal Corporation’s Red Hills Mine in Ackerman, Mississippi, began production in 2002. The Red Hills Mine delivers approximately 3.5 million tons of lignite coal per year to the nearby Choctaw Generation Power Plant. The daunting task before North American Coal has been to deliver ash levels appropriate for blending from six seams which have a wide variation in ash content and tough parting problems. North American Coal and Choctaw Generation Limited Partnership minimized the problem of fluidized bed boilers shutting down or derating on the power side of the operation with three of SABIA’s elemental coal analyzers. Through innovation and the use of the latest in commercially available high tech computer systems, the mine side has come up with a way to get real-time control of the quality of the lignite. By utilizing wireless remote laptop computers in the cabs of the Easiminer, 5230 backhoe, and shift supervisor truck that are connected to the display screens of an on-line operational SABIA nuclear elemental analyzer just downstream of the mine crusher, the operators have a direct hand in the quality of lignite sent to the Eurosilo storage system upstream of the power plant. This paper addresses the details of the application, including the technical details of the wireless system and the benefit to the operation.

Contents: Introduction to Red Hills Mine and Choctaw Generation Limited Partnership -Red Hills Power The Problem The Approach to the Problem The Applications Summary

Introduction

The Red Hills Mine and Red Hills Power Plant are relatively new projects. The Red Hills Mine is owned and operated by Mississippi Lignite Mining Company (MLMC), a subsidiary of The North American Coal Corporation. Red Hills Power is owned and operated by Choctaw Generation Limited Partnership (CGLP). Construction of the mine and plant began in 1998 with commercial operation accomplished in 2002. MLMC has a 30 year fuel supply contract with Choctaw Generation Limited Partnership at this facility.

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Figure 1. The Plant Layout An artist rendition of the Red Hill’s Power Plant. The major components of the lignite handling facility are as follows:

1) Truck dump hopper and primary crusher 2) Euro-silos (2) 3) Secondary Crusher Building 4) Tripper Deck and Day Silos 5) Limestone Building

The mine has 6 distinct seams ranging from 2’ – 5’ thick. Each seam is separated by inner burdens ranging from 10’ – 40’ in thickness. The qualities in these seams vary significantly. Each one presents certain challenges. The power plant is a single turbine 440 mw unit fired by 2 CFB boilers. Originally the power plant was designed to burn fuel with ash content up to 24%. Once commercial operation began, it was discovered that the practical upper limit for ash content is 18%. Any significant quantity of fuel with an ash content greater than 18% will cause the power plant to derate or go offline altogether. Historically this has happened on several occasions each year.

Figure 2. Lignite Seams at Red Hills Mine

Seams H through C from top to bottom are mined. The thickest seam mined is about 6 feet, with seams as thin as 6 inches mined also.

Lignite QualityLignite QualityAverage Quality For Mine Area 1Average Quality For Mine Area 1

Horizon TONS AS BT MO SU

COH 6,164.8 17.0 4960 41.79 0.57

COG 13,367.1 15.7 4970 43.10 0.59

COF 10,534.3 17.1 4880 42.03 0.51

COE 17,787.0 13.7 5240 42.75 0.35

COD 21,623.3 12.0 5460

1.02

42.66 0.36

COC 14,152.0 15.8 5210 42.16

Average 83,628.5 14.6 5,183 42.52 0.54

Figure 3. Mine Area 1 – As Delivered Qualities

These are the average as delivered qualities for Mine Area 1. The site will be in mine area 1 for the next 20 years. Some things to note about each seam are: H – Quality swings wildly. Center of pit has a pocket of high sulfur. G & F – Both of these seams have an inner seam parting that drops the overall quality dramatically. The mine has begun to separate these partings from the lignite in order to improve the quality. D & E – These are the best and most consistent seams at the mine. C – Burns very well in the boiler. This is apparently due to the fact that the ash mineral composition seems to be different than the other seams. The sulfur content is something that needs to be managed, but that doesn’t seem to cause too many problems.

rgest lignite quality roblem at the mine. The parting is very difficult to separate.

Figure 4. The Parting Problem at Red Hills Mine

F2 SEAM ~ 13.5% AshF2 SEAM ~ 13.5% Ash

PARTING ~ 42.0% AshPARTING ~ 42.0% Ash

F SEAM ~ 11.4% AshF SEAM ~ 11.4% Ash

This is the typical situation with the F and G Seams. It is the lap

handling system. The photo is taken from the top of the primary stockpile.

Generating 2 Eurosilos Station

Secondary Crusher

Figure 5. The Lignite Handling System - This is a photo of the lignite

Truck Dump and Primary Crusher

Figure 6. Primary Crusher and Feeder – C1 Conveyor

ontains ¼% accurate scale. In e past this scale has been used for payment purposes.

This is a photo from the back side of the truck dump hopper. The primary crusher is a stammler feeder breaker. Following the feeder breaker is C1 conveyor. It is a 60” belt with the tramp metal detector on it. C1 Conveyor also cth

C1 Conveyor

Truck Dump and Primary Crusher

Figure 7. Between the Primary Crusher and the Eurosilos

h

lt to the dual gamma ash and

icrowave moisture meters. There is a weigh scale on C1.

C1 ConveyorC2 Conveyor

After the C1 conveyor is the C2 conveyor. This is another 60” belt. A dual gamma asmeter and microwave moisture meter were located on C2, but were removed with the acceptance of the PGNA analyzer. The capacity of this system is supposed to be 1800 tons / hr. Actual production rates are usually around 1200 – 1600 tph. If lignite is being delivered with the 5230 backhoe production through the stammler can fall to 800 tph. C1 and C2 are constant speed belts (400 fpm). This causes the lignite thickness on the bevary. This was one source of error that caused the failure ofm

Figure 8. Lignite transfer points before the generation plant

first set of double yellow osts) is used to judge the quality of lignite going to the silos.

C2 Conveyor

Euro-Silos

This is another view of C2. C2 either discharges into Eurosilo #1 or onto Conveyor C3 which goes into Eurosilo #2. The C2 Analyzer (located at the p

Figure 9. The Eurosilos

ined capacity of the silos is 40,000 tons. he plant burns about 11,000 tons per day.

C2 Conveyo

r

C3 Conveyor

Euro-Silo 2 Euro-Silo 1

This is C2, C3, and the Eurosilos. The combT

Figure 10. Redundant lines after the Eurosilos

her

1 ½”. If necessary the entire ower plant can be operated off either C4A or C4B alone.

C4A & C4BC5A & C5B Secondary Crusher Building

After the silos the lignite conveyors are redundant. The first two conveyors are C4A & C4B. Each belt is 42”, constant speed belts. The rated capacity of each of these belts is 750 tph. The actual capacity is around 500 tph. Both Silos can be unloaded with eitbelt. From C4A&B the lignite is dropped into a surge bin in the secondary crusher building. The capacity of the surge bin is 100 tons. There are two secondary crushers that are fed by one common surge bin. The size coming out of the secondary crusher is rated at – ¼”, but it’s not uncommon to get fragments up top

Figure 11. Redundant conveyors (C5A and C5B) and samplers after the secondary

crusher

ce two belts, there are two pay scales and two primary cutters on the sampling

stem.

n. The

xcess lignite goes through a return conveyor and is dumped back on the belt.

veyor in the top left of the picture is used twice a year for materials tests on pay ales.

Secondary Sampler / Return System

C5A & C5B

Primary Sampler –1 on each belt

After the secondary crushers, the lignite goes onto C5A and C5B. These conveyors have the same basic dimensions and capacities as C4A & C4B. Contractually this is the lignite sales point. The pay scales are located on C5A & C5B as is the sampling system. Sinthere aresy The primary cutters on the sampling system converge into a common chute. The ligniteis crushed again, sampled again, and the composite sample is dropped into a cae The consc

Figure 12. C5A and C5B – looking towards the power plant

ry cutters. The excess return conveyor and hute system is on the far side of the cutters.

This is C5A & C5B along with the two primac

Figure 13. C5A and C5B – looking towards the power plant

ars. On g facility. The limestone is

neumatically conveyed directly into the boiler.

Tripper

Deck

C5A & C5B

Limestone Storage

Proposed Limeston

e Conveyor to C5A

& C5B

This is C5A & B as they go into the tripper deck in the plant. The entire power plant canbe operated off either C5A or C5B alone but normally C5A and C5B are dedicated to a boiler. The C5 conveyors drop onto C6 conveyors which run through tripper cthe left is the limestone storage building and dryinp

The Problem

.

complexity of the gnite coal makes for a unique challenge to the mining operation.

ed Hills Mine’s customer is Choctaw Generation Limited Partnership. They have:

rm, sole source, all fuels requirement contract with North American Coal (2033)

he Contractual Quandary

derated or shut own regularly if the ash in the delivered lignite was greater than 18%.

cification, but the power plant ften couldn’t burn it – it was a lose/lose situation.

ter e mine gets to ship 3.6 MTPY and the plant

ptimizes profits with higher uptime.

nd much wasted energy, the site gave up on this chnology. What they discovered was:

• ty information real time is extremely

The Red Hills Mine is the first and only lignite mine in Mississippi, with a mine capacity of 3.6 million tons per year. The mine has 6 different thin lignite seams, from 6 inches to 60 inches in thickness. The lignite is high moisture at about 43% and low BTU at 5100There are three overburden removal operations: truck-shovel removal, dozer push, anddragline. The site receives an average of 52” of rain per year. Theli R

Net Output 440 megawatts 2 Circulating Fluidized Bed Boilers (CFB’s) Long-Term Power Purchase Agreement with TVA (2033)

Long-Te

T The economics for a successful operation for the mine is to ship at least 3.6 million tons of lignite to the plant each year. The original contract required ash no greater than 23.5% by weight. However, startup conditions were such that the plant had to bed The dilemma = the mine was meeting the original speo The solution = find a way to control the quality of the lignite so that it is never greathan 18% ash – everyone is happy! Tho As a result of this dilemma, the mine decided to try a dual gamma ash gauge with anassociated microwave moisture meter to get control of the quality. The system was installed on 4/24/02. Some results were encouraging, but the site soon discovered thatthe ash and moisture results drifted with things like belt loading and lignite type from seam to seam. After years of false hope ate

The ability to know lignite quali valuable to the staff of the Red Hills Mine.

Incorrect real time • lignite quality information is worse than no real time information at all.

Dual Gamm a mining due to: rate.

• ble to variations in bound moisture, belt loading and changes

from seam to seam.

sis is an online easurement technology that has a long track record in coal and cement.

Figure 14. The SABIA Analyzer mounts on existing conveyors

a sh meters have a very limited application in lignite

– Inability to handle variations in lignite flow – Inability to handle multiple lignite sources.

Microwave moisture meters do not work in lignite where moisture exceeds 30% and are very vulnera

As a result, the site went back to the drawing board and decided PGNA (Prompt Gamma Neutron Activation) might be the answer. PGNA nuclear elemental analym

he Approach to the Problem

, the mine determined that PGNA was an attractive approach to their dilemma because:

• e lignite, the site can potentially

• ing it can then estimate BTU lculations

2O3, Na2O, CaO, TiO2, K2O, N, Cl • Calculates BTU, SO2/mmBTU, etc

nd cons of products from three different vendors, ut chose to go with SABIA because:

ve to requests

ction. Minimal conveyor frame modification

curate and robust • SABIA was willing to put a unit on site on 6 month trial lease

ecided ess, which led to the

cquisition of a total of three analyzers as described below.

T After considerable research

By knowing the elemental makeup of thaccurately estimate the % ash If used in conjunction with an accurate moisture readthrough Moisture and Ash Free (MAF) ca

• Directly Measures Ash, Sulfur, Moisture • Directly Measures SiO2, Al2 O3, Fe

The mine site next discussed the pros ab

• Very responsi• Lowest Cost • Strong customer recommendations • Modular Constru• Strong Pedigree • Web Browser based software • Willingness to do a Demonstration Project • Experimental PGNA Moisture Meter – promised to be more ac

As a result of the extensive evaluation, Red Hills Mine and Choctaw Generation dto give the SABIA analyzer a tryout. This tryout was a succa

Figure 15. The trial analyzer located on C5A

SABIA Analyzer C5A

C5A Sweep Arm Mechanical Sampler

he Applications

es. The analyzers were installed as own in the layout of figure 16 shown below.

nd of the process on the C2 Belt just downstream f the Truck Dump/Primary Crusher.

he analyzers are used as follows:

ples in the

it

bed flop situations by making adjustments in

sponse to the reported analyzer results.

et im

omer to provide nalyzer outputs to feed directly into their existing data system.

T Three analyzers were acquired on five-year leassh

The first analyzer installed was the C5A analyzer. It was installed on a six-month trial basis. The success of the trial led to the acquisition of a second analyzer for the C5B Belt and an analyzer to be used at the front eo T C5A Analyzer – As the trial analyzer, this first system was used to monitor incoming lignite fed on conveyer C5A. The unit was installed in August, 2006 with a six month trial lease. Initially the analyzer was calibrated using known static samanalysis region. This calibration was completed as part of the overall installation/commissioning process which took about six weeks. It should be noted that even though this calibration was preliminary (based on a very limited data set), the unbegan almost immediately to serve as a useful trending device. The operators in the control room began watching the ash trend charts and before too long were able to avoidwhat would have normally been derate or re Once the unit was operating, additional dynamic comparative data samples were acquiredusing the existing sweep-arm mechanical sampler on the C5 belts. Given the number of seams and the large number of possible combinations thereof, it took several weeks to ga data base meaningful enough to implement a robust calibration. During this interperformance optimization period, the vendor worked with the custa

Figure 16. From pit to boiler, showing analyzer placement

rate,

fuel avoid the vast

ajority of fuel related problems before they appear in the boilers.

sult

eb browser based machines with separate IP addresses.

om

l displays were mounted using Ram Mount Clip System in key vehicles used in the Pit.

C5B Analyzer – Now the C5A and C5B analyzers monitor the lignite flow to the two boilers. The two Eurosilos are loaded so that Eurosilo 1 fuel is less than 15% ash and Eurosilo 2 is less than 20% ash. The control room operators have the ability to make limited adjustments to the blend ratio depending on the real-time analysis results from theanalyzers. The plant has 4 day silos for each boiler. With full day silos at full burnthis represents about 5 to 6 hours of fuel. Before the C5A and C5B analyzer were commissioned, when a problem accrued there could still be six or more hours of badin the day silos. With the analyzers in place preemptive changes canm C2 Analyzer - The C2 Analyzer now plays a key role in the operation. The data from the C2 Analyzer is used in real time to make mining modifications that have a material reon the quality of the lignite going into the Eurosilos. The information from the C2 Analyzer is available on the Red Hills Mine Intranet because all the SABIA analyzers are w Red Hills Mine used its existing wireless network in the Pit so all the information frthe analyzer would be available to the mining operation. As shown in figure 16, a wireless router in the main mining office is linked to a Motorola Mesh Wireless Network in the pit. Panasonic Tuff Book Series Laptops with swivea

One laptop was mounted in the Easiminer, one in the Caterpillar 5230 backhoe, and one

the pickup of the shift supervisor. See the figures below.

Figure 17. The Overall Analyzer Status Screen for C2 Analyzer

in

Figure 18. The Red Hills Easim er and Haul Truck being loaded in

Figure 19. The Rolling Average results display in the Easiminer

e display in the Easiminer Figure 19 above

asis. The perators typically are making decisions on the 10 and 40 minute results.

Figure 20. A screenshot of the rolling averag The analyzer result display used by the operators in the Pit is the running average displayscreen. This screen is a user-configurable table. In this case Red Hills has set the table for running average results displayed on a 5min, 10min, 40min, and 4hour bo

Figure 21. The Caterpillar 5230 Backhoe filling a dirt truck.

e loader sitting up on the lignite seam and the haul truck being loaded on the lower level.

Lignite loading operates in the same manner with th

Figure 22. The display screen in the Caterpillar 5230 Backhoe

The lignite haul operation is focused on two areas of interest: Maximizing seam recoveand ensuring a consistent product to the Eurosilos. This can be extremely challengingworking with shallow/rolling seams or unexpected changes in seam quality. The C2 Analyzer has become a key part of the mining operation with two fundamental control actions available to ensure that the lignite in the Eurosilos meets the low and high ash constraints necessary to ensure smooth boiler operation downstream. For the loading machine (either the Easiminer or 5230), the operator simply adjusts his mining depth ifthe analyzer shows that the lignite being mined is too far beyond the target quality fosending to the Eurosilo. If the operator is certain he is in seam but that the lignite is simply of a quality beyond the acceptable target another loader swings into action using one of two divergent ash quality stockpiles in the Pit area. In conjunction with the trucks delivering lignite to the truck dump from the pit, this loader provides alternate loads to atruck from the stockpile to the truck dump. In this way the average lignite delivered to the Eurosilos meets the quality target, resulting in a much more uniform lignite quality delivered to the boilers. All of the information available to the operators is also avaito the mine shift supervisor in his pickup truck or in the office. Via radio, the shift supervis

ry

r

lable

or orchestrates the foregoing adjustments depending on what the analyzer is eing.

ummary

f ard with

y

d shutdowns, all of which adds impressive profits to the bottom line for both companies.

anks to the many contributors on both the mine and power plant side of the project.

se S

Although already favorably impressed with the trending capability of PGNA technology, Red Hills Mine and Choctaw Generation became officially “sold” on the technology as a result of the formal acceptance test of the trial unit and the related significant reduction obed flops and plant derates. As Red Hills Mine and Choctaw have moved forwthe new technology, they have learned how to use the available lignite quality information to provide fuel to the fluidized bed boilers in such a way that they not onlcontinue to eliminate unplanned shutdowns, but they also have significantly reduced “derated” operational modes and are delivering fuel in a manner that optimize boiler operation and extend periods between schedule

The success of this project warrants special th

REFERENCES

Fossil Operation & Maintenance Information Services Conference, eptember 2005.

Controls Handbook, Editor-Gregory K. McMillan, Fifth Edition, cGraw Hill, 1999.

ur P., “On-line Analyzers Improve Coal Quality”, Coal Age Magazine, p.52, ne 1992.

to On-line Coal Analyzer

echnical Conference, St.Louis, MO, November 2004.

C. & Lee, Brenda, “On-line Analysis Evolves”, Coal Age Magazine, .22, March 1977.

e Analysis Can Boost Profits from Blending”, Coal Age agazine, p.48, June 1987.

Jancauskus, Joe, Linsberg, Mark, “Real-Time Coal Analysis at J.M. Stuart Station - A Progress Report”, S Proctor, R.J., “On-line Prompt Gamma Neutron Activation Analyzers”, Process/Industrial andM Sanda, ArthJu Snider, Kurt, Woodward, Richard. “Using an On-Line Elemental Coal Analyzer Reduce Lost Generation Due to Slagging”, InternationalT Woodward, Richardp Zumberge, James F., “On-linM