Principal Research Results

Development of Technique for Evaluating Coal Adaptability to Power Plants−Evaluation Method for Grindability and Emission Characteristics of NOx andUnburned Carbon in Fly Ash in Partial Load Combustion−
BackgroundIn pulverized coal thermal power, it is important to keep the coal supply stable and to control the fuel cost. For that purpose,the use of coal of various properties up to now, without the experience is necessary, the adaptability to the power plant of these coals
is appreciable beforehand, and the technology that the operation indicator corresponding to the coal property can be presented is indispensable. Therefore, “evaluation system of coal adaptability to power plants which can make clear the adaptability of new coal fromthe coal properties and the combustion condition was developed for the case of non-blended and blended full load combustion ＊ 1,＊ 2.
However, enhancing the functions to further raise accuracy and the partial load combustion is indispensable to improve the practicalityof this system.

Objectives
To make the high accuracy system to be able to predict the pulverized coal particle size for grindability evaluation, and toenhance the evaluation system for the grindability and emission characteristics of NOx and unburned matter in fly ash into the partial
load combustion.

Principal Results
1. Improvement of the accuracy on the grindability evaluation system and extension of it into the partial load combustion
The HGI ＊ 3, fuel ratio, coal feed amount and rotation number of rotary classifier were able to be extracted as the main factor
that influenced grindability of coal (power and rate of 200 mesh pass ＊ 4 of the mill) based on the data of a real power plant. By theanalysis on correlation of these influence factor and grindability (Fig.1), the technique to evaluate the grindability in various load conditions was built with sufficient accuracy as a function of HGI, coal feed amount and rotation number of rotary classifier (Fig.2, 3).
2. Extension of the evaluation systems for emission characteristics of NOx and unburned matter in fly
ash into the partial load combustion
The applicability of the evaluation system for the NOx and unburned matter in fly ash under full load combustion to the partial load combustion was examined and its possibility recognized for the unit, whose combustion condition was wide for full load
(Fig.4). On the other hand the evaluation accuracy was reduced in the units, whose combustion conditions at the partial load weremuch different from that of the full load combustion. In this case, by deriving the new formula that applied the rate of partial load, evaluation on them was enabled with the same accuracy as the full load combustion (Fig.5).
The above-mentioned result is added, and a whole of the system that has constructed it so far is shown in Fig.6. The coal
adaptability evaluation system, which can make clear the adaptability of coal to power plants in various operation conditions from theevaluation items of spontaneous combustion, grindability, emission characteristics of NOx and unburned matter in fly ash and ash
properties was completed.

Future Developments
The shape and adhesion of the ash and trace element emission characteristic will be added as an evaluation item of coal
adaptability, and higher performance of the system will be aimed at in the future.
Main Researcher: Hiromitsu Matsuda,
Senior Research Scientist, Fuel and Combustion Engineering Sector, Energy Engineering Research Laboratory
Reference
Hiromitsu Matsuda, 2004, “Evaluation of coal adaptability to power plants (Part5) -Evaluation method for grindability and emission
characteristics of NOx and unburned carbon in fly ash in partial load combustion-” , W03306 (in Japanese)＊1：Coal adaptability evaluation system is the one to evaluate adaptability from 4 evaluation item of “spontaneous combustion”, “grindability”,“emission characteristics of NOx and unburned matter in fly ash” and “fly ash property” to the power plant., dentyukenhoukoku, W99302(2000)＊ 2：dentyukenhoukoku, W01302 (2002) dentyukenhokoku, W03038 (2004)＊ 3：Hardgrove grindability index＊ 4：Weight ratio of pulverized coal that passes the 200meshes sieve (correspond to particle diameter 75μm or less)48

C. Harmonization of energy and environment

90
80

Rotation rate ofrotary classifier
low
middlehigh
middle
high

HGI

120

５３５３
５３
６０６０7060Mill load 100%
Mill load 50%
Mill load 135%90ｎ Standard var.
DataWhole 121
0.106
0.109
Full load 53
Partial load 680.078

5000204060
Coal feed[t/h]80128Dataｎ Standard var.
0.115
Whole 116
0.112
Full load 50
Partial load 66
0.119400100Mill load 100%
Mill load 50%
Mill load 135%

1660

304020

HGI：40〜80
Fuelratio：0.94〜2.23

Predicted[kwh/t]

Rate of a 200-mesh pass[%]

▲
●
■
●
■

Predicted[%]

KEY

100

3060901200

Measured[%]48121620

Measured[kwh/t]

Fig.1 Relation of coal feed andrate of 200-mesh pass

Fig.2 Evaluation accuracy of200-mesh pass rate

Fig.3 Evaluation accuracy ofmill power

Grindability condition's (It is coal feedin figure)influence on rate of 200 meshpass was clarified

It was clarified that rate of 200 mesh pass
could be accurately predicted from HGI, coalfeed, and rotation number of rotary classifier.

It was clarified that mill power couldbe
accurately predicted from HGI, coal feed,and rotation number of rotary classifier.

15.0

Predicted[%]

12.0
9.0

Coal feed amountRotation numberof rotary classifier

Non-blend / Full load
Blend / Full load
Blend / Partial load

3.00.00.0

3.06.09.0

12.0

Fig.4 Evaluation accuracyof NOxformation
It was clarified that NOx formation in partial
load combustion could be accurately evaluatedfrom prediction equation for full load.

Prediction[%]

2.5

Prediction of the rate of
200-mesh pass and the mill
power was enabled frommill operation condition

Rate of a 200-mesh pass

The rate of two-stage combustionand excess oxygen concentration
change by partial load combustion
are taken into consideration to an
evaluation system.

Full load
Partial load

2.0

O/C

Grindability
Spontaneouscombustion

15.0

Measured[%]Mill powerCombustion
Comcondition

Fuel ratio,
Ｎcontents

NOx and unburned matterformation characteristics

NOx

Unburned matter

Fuel ratio

1.5
1.0：Input item

0.5

0.0

0.5

1.0

1.5

2.0

2.5

Fig.6 Evaluation system of coal adaptability to power plant

Full load
Partial load2.0＊）The amount of the MB adsorption: When it uses the coal ash
as a concrete mixture material, the amount of the methylene blue
adsorption is index of the amount of the surface-active agent
adsorbed by the active carbon in the coal ash.

1.5
1.00.5(2) Predictionequation
for partial load

0.00.00.5

1.01.5

Methylene blue
absorbed amount＊）：Examination in this phas：Evaluation program

2.5

Measured[%]Fly-ash property：Output item

(1) Predictionequation
for full load

0.0

Prediction[%]Coal property
HGI,Fuel ratio

6.02.0The evaluation system, which can predict the spontaneouscombustion, grindability, emission characteristics of NOx
and unburned matter in fly ash and ash properties in various
operation conditions of power plant from the coal property
and combustion condition was established.

2.5

Measured[%]Fig.5 Evaluation accuracyof unburned matter
It was clarified that unburned matter formation in partial load
combustion could be accurately evaluated from prediction
equation, which applied the rate of partial load.

49