Part 2 CCT Overview
Environmental Protection Technologies (Technologies to Effectively Use Coal Ash)

5C1. Coal Ash Generation Process and Application Fields
Technology overview

1. Background and general status of generation process
Coal ash has, since it was commercialized as a cement

Powertransmission

admixture in the first half of the 1950’s, been widely used in
Steamapplications such as a raw material for cement, cement mixtures,Households/factories

roadbed material, backfilling material, and embankment material,
Steam turbine

finding its way mostly into the cement sector, particularly, as aGeneratorTransformer

clay-alternative raw material for cement.
BoilerCoal combustion methods are roughly divided as follows:

Smoke stack

Coal-fired power plant(1) Pulverized coal combustion (dry-type)
Economizer(2) Stoker firingAir
pre-heater(3) Fluidized-bed combustion

Electrostatic
precipitator(4) Circulating fluidized-bed combustion
Clinkerhopper

Fly ash(85-95%)

Breaker

2. Generation rate
According to a survey conducted by the Center for Coal
Utilization in 2003, the coal ash generation rate in Japan was
9.87 million tons a year, up 6.8%, or 630,000 tons, from theBottom ash(5-15%)

preceding year. Most coal-fired boilers for the electric utility

Graderindustry are combusting pulverized coal. In addition, in generalindustries, 132 One-MW or larger coal-fired boilers are inDe-wateringtankoperation, a majority of which combust pulverized coal. In terms

SiloSilo

Siloof boiler capacity (steam generation rate), 50-ton/hr or smaller
Baggerboilers are mostly of a stoker combustion type while many of theHumidifier

Humidifier

100-ton/hr or larger boilers combust pulverized coal. Figure 2shows changes in the rate of coal ash utilization and generation
Dump truck

from electric power utilities and One-MW or larger installed power

Ship

Truck

Jet vac truck Dump truck

Jet vac truck Dump truck

Fig. 1 Coal ash generation from a pulverized coal-fired boiler
Source: Japan Fly Ash Association

generation plants in general industries from 1993 through 2003.

3. Composition of coal ash
In Japan, 90% or more of the coal ash generated is fromRate of utilization

pulverized coal combustion, dwarfing the 7% or so from fluidized-Rate of generation

bed and some 1-2% from stoker combustion. The generation ratio
Coal ash (thousand tons)of fly ash to clinker ash (bottom ash) is 9:1.
As for the shape of coal ash particles, low-melting point ash isoften globular while much of high-melting-point ash isindeterminate in shape. The average grain size of fly ash frompulverized coal combustion is approximately 25 m, similar to silt
in fineness, between finer clay and coarser fine-grained sand foruse as a soil material.
The chemical composition resembles mountain soil, with two
inorganic components, silica (SiO2) and alumina (Al2O3),comprising 70-80% of the total composition. Other than these,Yearferric oxide (Fe2O3), magnesium oxide (MgO), and calcium oxideFig. 2 Changes in coal ash generation and utilization rates(CaO) are also contained in slight amounts. In Japan, thecomposition of coal varies widely since 100 or more varieties ofcoal are imported from all over the world.

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Clean Coal Technologies in Japan

4. Application fields
Table 1 shows the effective utilization of coal ash in FY2003 byare not bright. To cope with a likely increase in coal ash in thefield. Usage in the cement industry is increasing annually. Of thefuture, expanding utilization in other sectors will be important. In

8.38 million tons used, the cement industry accounted for 6.33

particular, the civil engineering field is expected to use more coal

million tons, or 75.5%. Recently, however, cement production has

ash because of its high potential for consuming large quantities.

been declining and the prospects for substantial future increases

Table 1 Breakdown of fields for the effective use of coal ash (2003)
Electric utilities

TotalConstruction

Agriculture/forestry/fisheries

OthersTotalComposition
ratio (%)

Rate ofutilization

Composition
ratio (%)

Rate ofutilization

Composition
ratio (%)

4,354

71.32

1,522

66.90

5,876

70.12

Cement mixture

149

2.44

159

6.99

308

3.68

Cement admixture

95

1.56

48

2.11

143

1.71

4,598

75.32

1,729

76.00

6,327

75.50

Foundation improving material

138

2.26

104

4.57

242

2.89

Civil work

103

1.69

25

1.10

128

1.53

Power supply construction

79

1.29

00.00

79

0.94

Roadbed material

50

0.82

110

4.84

160

1.91

Asphalt/filler material

90.1500.00

90.11

Coal mine filling material

204

3.34

00.00

204

2.43

Sub-total

583

9.55

239

10.51

822

9.81

Construction materials (boards)

213

3.49

164

7.21

377

4.50

Artificial light-weight aggregate

00.00

00.00

00.00

Secondary concrete product

18

0.29

10.04

19

0.23

Sub-total

231

3.78

165

7.25

396

4.73

Fertilizer (including snow melting agent)

53

0.87

26

1.14

79

0.94

Soil conditioner

110.18

82

3.60

93

1.11

Sub-total

64

1.05

108

4.75

172

2.05

Sewage treatment agent

40.07

10.0450.06

Steel making

130.21

80.35

210.25

Others

612

10.02

25

1.10

637

7.60

Sub-total

629

10.30

34

1.49

663

7.91

6,105

100.002,275

100.008,380

100.00Application
Cement raw material

Sub-total
Civil engineering

General industry

Rate ofutilization

Field
Cement(Unit: thousand tons)

Total

References

1) The Center for Coal Utilization, Japan (now known as JCOAL): National Coal Ash Fact-Finding Survey Report (2003 results), 2005.
2) Environmental Technology Association/the Japan Fly Ash Association Coal Ash Handbook 2000 Edition, 2000.
3) Nobumichi Hosoda: CCUJ, Coal Ash Utilization Symposium lecture collection, 1998.
4) Natural Resources and Fuel Department, the Agency for Natural Resources and Energy: Coal Note (2003 edition), 2003.

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