(573a) Developments of Coal Fired Power Generation Processes in Japan after the First Oil Crisis (1973)

Developments of coal fired
power generation processes in Japan after the first oil crisis(1973).

 Shigekatsu Mori

Emeritus Professor of Nagoya University

2-17-4 Minamigaoka , Nisshin, Aichi ,470-0114, Japan

e-mail : Shigekatsu-m@mf.ccnw.ne.jp

 Forty-four years have passed during my
contribution with coal conversion technologies. In this presentation,
developments of various coal fired power generation processes in Japan are
introduced. Additionally, recent Japanese situations of power generation system
are also briefly introduced.

1.   Atmospheric pressure bubbling-bed type
fluidized-bed boiler

 Most of Japanese coal conversion projects
were started after the first oil crisis.

 Until 1973, main power generation plants in
Japan were oil fired plant and therefore the replacement of oil with coal were
strongly requested.  Then our Japanese
chemical engineering group started the project to develop the fluidized-bed
coal combustion process with desulfurization by lime-stone. Fundamental stages
were passed through in a short term and the national project was started
immediately.  Both 20t/h pilot plant
and also 160t/h (50 MW) demonstration plat operations were successfully
achieved and then 350MW oil fired power generation plant was replaced by coal
fired FBC plant.  To  keep same power generation capacity as the
original oil fired plant, stacked up structure was newly adopted as the FBC
plant.  Around the same time the
global warming problem generated by carbon dioxide emission had become the significant
problem. Then fossil power efficiency of power generation plants had been
emphasized.  However, the fossil
power efficiency of A-FBC plant was sub critical level since its bed
temperature was limited less than 1273K.  Then the development of A-FBC coal fired
power generation plant was suspended.  However, bubbling fluidized bed
combustion technologies have been adopted for relatively small scale incineration
plants of municipal wastes. 
Recently, FBC plants have been also widely adopted as power generation
process of woody biomass in Japan.

2.  Development of pulverized
coal fired power generation process.

 In 1960fs, a few pulverized coal fired
power generation plants had been operated and their maximum unit capacity were
250Mw and their steam condition were sub-critical, then their fossil power
efficiency(LHV) were 37 to 39%. 
After the energy crisis,   pulverized coal fired power plants were
thoroughly developed. The super critical condition was achieved and their
efficiency were 39 to 40% in 1981. Their maximum unit capacity was reached to
500Mw in 1981 and 700Mw in 1988. In 1990, the ultra-super critical condition
and 100MW was achieved and their efficiency were 41 to 43%.   Their maximum unit capacity was reached
1000Mw in1990 and now it has been 1050Mw. More important achievements of their
developments were accomplishment of air pollution control processes. Such as, electrostatic
precipitator was adopted as the dust collector, wet lime plaster method was
adopted as the desulfurization process and dry ammonia selective catalytic
reduction was adopted as the denitrification process. Although the most
attractive advantage had been its cheapest price, most important principal problem
of coal power generation has been its emission of carbon dioxide gas. Then,
developments of its improvement technologies have been still most important
tasks of the power generation process in these days.

3.  Gas-turbine combined cycle power
generation process of liquified natural gas.

In 1984, gas-turbine combined cycle power generation process
was adopted as the power generation process of natural gas in 1984. The
combined cycle was constituted with gas turbine generation process and with waste
heat recovery steam boiler system. This engineering achievement had been
extremely effective to introduce the power generation process of imported
liquified natural gas(LNG) from overseas. The thermal efficiency of the gas
turbine combined cycle was determined by the gas turbine inlet temperature. In
1984, the gas turbine inlet temperature was 1473 K and it thermal
efficiency(LHV) was 48 %. Turbine inlet temperature was limited by heat
resistant properties of turbine blades and then aggressive research works on
the material development of turbine blades had been continued. Then turbine
inlet temperature had been increased and then thermal efficiency had been
raised up, such as; turbine inlet temperature was 1633 K and its thermal
efficiency(LHV) was 49% in 1994, turbine inlet temperature was 1773 K and its
thermal efficiency(LHV) was 58% in 1996, thermal efficiency(LHV) was reached
60% in 1998, turbine inlet temperature was 1873K in 2011 and its efficiency(LHV)
was 62%.

4. 
Entrainment
type coal gasification process for integrated coal combined cycle

Just after the successful
operation of gas-turbine combined cycle power generation process of LNG, developments
of integrated coal slagging gasification combined cycle(IGCC) were started. Two
types of coal slagging gasification processes were developed, such as the air
blown slagging coal gasification and the oxygen blown slagging coal gasification.
Dry pneumatic conveying systems of coal were adopted in both plants.

4.1    
Integrated
air blown slagging coal gasification combined cycle¹⁾.

Based on the fundamental research with 2t/d process
development unit, 200t/d pilot plant was operated in 1991 to 1996. 1700t/d and
250Mw demonstration unit was designed and constructed. Then the demonstration plant
operation was successfully finished in 2012. From 2013, Commercial operation
had been started as 250MW Nakoso No.10 plant. Specification of this plant are
mentioned as follows, such as: capacity is 250MW gross, coal consumption is
approx.1700t/d, gas turbine is 1473K class(50Hz). Efficiency gross is 48%(LHV)
and net is 42%(LHV). Flue gas properties are achieved as follows, such as;
particulates < 4 mg/m³N , SO_x < 8ppm, NO_x
< 5ppm

4.2. Integrated oxygen blown slagging coal gasification combined
cycle²⁾.

 Based on the operation experience of
10t/d test plant (HYCOL plant) during 1990-1993, 150t/day of 2.5MPa pilot plant
(EAGLE plant) was constructed and operated in 2002- 2013. This entrainment
slagging coal gasifier had two stage oxygen blown gasification burners in the
single gasification room. Slugged coal ash was quenched in bottom quencher by water
and discharged. Since this plant was oxygen blown gasification process, both nitrogen
and CO₂ concentration in the product gas was limited and then CO and
H₂ were enriched.  Very
low emission level of product gas was achieved, such as: SO_x ,
Halogen and Ammonia were kept less than 1ppm and dust was kept less than 1mg/m³N.
Based on these excellent operation experience, 1180 t/d, 166Mw demonstration
plant ( Oosaki-Coogen plant ) was constructed and gas purification test
facilities were configured with COS conversion and removal unit and also with H₂S
adsorption unit . The demonstration and semi-commercial operation was started
in 2017. The demonstration of CO2 removal and recovery operation will be also
challenged as the second stage.

5. Recent situations of
Japanese power generation system

 Resent
situations of Japanese power system will be tried to be introduced briefly.

However, great uncertainty factors make the
situation extremely unclear, then it is very difficult to clearly predict the
situation of only half year later, then some dominant controlling factors of
the situation are only mentioned here.

1) After
Fukushima nuclear power plants were completely destroyed by the great tsunami
caused by east Japan great earth quake disaster.  In Japan,16 nuclear power-  plants were presented and total their
capacity was 44,264MW. However, although Japanese government has promoted their
restart strongly and even Japanese ministry of environment also promoted them
to reduce emission of carbon dioxide, still major peoples have not agreed with
their restart and only two plants have been operated now.

2) The trends of the world and Japanese
people about worldwide green-house problem and CO2 reduction have been quite
important. Japanese ministry of environment has disturbed the construction of new
coal fired power generation plants strongly.

3) World supply-demand relationship of
energy resource and the price of oil and LNG are also important factors since
all of these resources are completely imported from foreign countries.

Acknowledgments

Author express great gratitude to AIChE and
Society of Chemical Engineering of Japan and also to Professor LS Fan and
Professor Nobusuke Kobayashi for their great contribution on the organization
of this session.

Literature cited

1)    
Nunokawa, M.: Paper presented
in International Conference on Power Engineering (2013)

2)    
Aiso, K.: Paper presented in
Subcommittee of power generation from coal, 9th China-Japan Forums on energy
conservation and environment (2015)