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 1960fs, 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 , SOx < 8ppm, NOx < 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: SOx , 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)
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