Clean Coal Technologies in Japan

2A3. Internal Circulating Fluidized-bed Combustion Technology (ICFBC)
Research and development: Japan Coal Energy Center; Ebara Corporation; Idemitsu Kosan Co., Ltd.
Project type: Coal Production and Utilization Technology Promotion Grant
Period: 1987-1993

Technology Overview

1. Features
The basic characteristics of ICFBC are described below:

3) Low polluting

I. Uniform temperature in fluidized-bed, owing to the swirling flow

NOx and SOx emissions are significantly decreased withoutof sand.

special environmental modifications. For the fluidized-bed boiler,

II. Easy discharge of non-combustibles, also owing to vigorous

desulfurization takes place mainly in the furnace. However,

movement of sand.

ICFBC does not have a heat transfer tube in the fluidizing

III. Ability to control the temperature of the fluidized-bed bysection, so the boiler does not cause wear on the heat transfer

adjusting the heat recovery from the fluidized-bed.

tube in the bed. Because of this, silica sand can be used as theBased on these, ICFBC has the following features:

fluidizing material for ICFBC, instead of soft limestone. As a1) Adoption of various fuels

result, ICFBC needs minimum quantities of limestone as anSimilar to CFBC, ICFBC is capable of using not only fossil fuels,

intrafurnace desulfurization agent. The desulfurization efficiency

such as high-grade coal, oil, and gas, but also low-grade coal,of ICFBC approaches 90% at a Ca/S molar ratio of around two,biomass, sludge, waste plastics, and waste tires.

though the efficiency depends on the coal grade, the amount of2) Control of bed temperature

limestone applied, and the temperature of the fluidized bed.

Since the overall heat transfer coefficient varies almost linearly

Denitration is conducted through a two-stage combustion

with the variations in the air-flow rate in the heat recovery

process: the reducing combustion at the fluidized-bed section,chamber, the quantity of recovered heat is easily regulated

and the oxidizing combustion at the freeboard section. The

through the control of the air-flow rate. In addition, control of theunburned carbon from the boiler is collected by the high-quantity of recovered heat regulates the temperature of thetemperature cyclone installed at the exit of the boiler. The

fluidized-bed. Since the control of the recovered heat iscollected, unburned carbon is recycled to the boiler to increase

performed solely by varying the air-flow rate, adjusting the load isthe denitration efficiency.

very simple, which is a strong point of ICFBC.

4) Space-saving, ease of maintenance
Similar to CFBC facilities, ICFBC facilities do not need separate
units for desulfurization, denitration, and fine-fuel crushing.
Therefore, ICFBC facilities are space saving and easier tomaintain because trouble-spots are minimized.

2. Technology overview
Figure 1 shows an overview of ICFBC. The technology uses silica
sand as the fluidizing material. The fluidized-bed is divided into

Freeboardthe main combustion chamber and the heat recovery chamber byPrimary
combustion
chambera tilted partition to create a swirling flow inside the main
combustion chamber and a circulation flow between the main
combustion chamber and the heat recovery chamber. A
circulation flow is created to return the unburned char andunreacted limestone from the cyclone at the exit of the boiler toHeat
recoverychamberthe boiler.
1) The swirling flow in the main combustion chamber is createdby dividing the window box in the main combustion chamber into
three sections, and by forming a weak fluidized-bed (moving bed)at the center section, introducing a small amount of air whileforming strong fluidized-beds at both end-sections andintroducing large volumes of air. As a result, the center section of
the main combustion chamber forms a slow downward moving
bed, and the fluidizing material, which is vigorously blown up fromboth ends, settles at the center section, and then ascends at bothFig. 1 Overview of ICFBCend-sections, thereby creating the swirling flow.
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Part 2 CCT Overview
Coal-fired Power Generation Technologies (Combustion Technologies)

2) The circulation flow between the main combustion chamber

3. Study sites and application fields

and the heat recovery chamber is created by the movement

Examples of locations and companies using coal-fired ICFBC

described hereafter: A portion of the fluidizing material, which isinclude: Chingtao, EBARA CORP. (10 t/hr); Jiangsan in China (35vigorously blown up at both end-sections in the main combustiont/hr); and Nakoso, Nippon Paper Industries Co. (104 t/hr).

chamber, turns the flow direction toward the heat recovery

Examples of locations and companies using ICFBC using

chamber at a position above the tilted partition. The heat recovery

industrial waste as the fuel include: Motomachi, Toyota Motorchamber forms a weak fluidized-bed (downward moving bed)

Corp. (70 t/hr); Tochigi, Bridgestone Corp. (27 t/hr); Fuji,

through the circulation bed air injected from under the chamber.

Daishowa Paper Mfg. Co., Ltd. (62 t/hr); Amaki, Bridgestone

Accordingly, the fluidizing material circulates from the main

Corp. (7.2 t/hr); and Akita, Tohoku Paper Mfg. Co., Ltd. (61.6 t/hr).

combustion chamber to the heat recovery chamber, and again toIn Shizuoka, Chugai Pharmaceutical Co., Ltd. is operating an

the main combustion chamber from the lower part of the heatRDF-fueled ICFBC site (3.7 t/hr).

recovery chamber. Since the heat recovery chamber is equippedwith heat transfer tubes, the circulation flow recovers the thermalenergy in the main combustion chamber.

4. Development period3) The circulation flow from the cyclone at the exit of the boiler

ICFBC was developed in 1987, and was further developed

passes through the cyclone or other means to collect unburnedand validated as a low-polluting, small-scale, and high-char, emitted fluidizing material and unreacted limestone, andefficiency fluidized-bed boiler for multiple coal grades in thethen returns to the main combustion chamber or the heat"Study of Fluidized-bed Combustion Technology," conducted

recovery chamber, using a screw conveyer, pneumatic conveyer,by the Coal Utilization Technology Promotion Grant project ofor other means. The circulation flow is extremely effective in

the Ministry of International Trade and Industry over theincreasing the combustion efficiency, decreasing the generation

course of six years from 1988 to 1993.

of NOx, and improving the desulfurization efficiency.

5. Progress and development results
Although ICFBC was initially developed to use high calorific value
industrial waste, it was improved to use solid fuel with a highcalorific value and has been developed as a coal-fired boiler. A
boiler plant was constructed in China, a country with abundantcoal reserves, in the city of Chingtao, a manufacturing base.
Recently in Japan, wood-based biomass has been used as a fuelin some cases. However, a further reduction in up-front
investment costs is required to disseminate the technology toSoutheast Asia and other areas rich in biomass resources andlow-grade coal.
Photo 1 ICFBC site

SteamBoiler
drum

Dry coalStack
Dry
feedsystem

CoalbunkerLimestone
Pulverized coal
Slurryfeedsystem
Air compressor

CWP
mixingsystem

Air
heaterDepressurizing
unit

PICFB

Crusher

Hot gasfilter

IDF
SteamBagfilter

Waste heatboiler(Gas cooler)

CWP pump

Ash CoolingpipePressure vessel

Boiler water
circulationpump
Hot blast generator

Deashingsystem

Pneumatic ash transport system

Fig. 2 Flowchart of PICFBC model test plant27Ash