Published on MHI Graph (July 2013 Issue)
PRODUCT EXCELLENCE[ TRANSPORT & SPACE ]
Clean Production of Energy Using IGCC (Integrated Coal Gasification Combined Cycle).
The first domestic IGCC plant was entirely resourced by just one company, with MHI supplying everything including the basic design, the gasifier, the gas turbine and the plant engineering. In the test operations started in September 2007, it achieved high net thermal efficiency (Note) (42.9 percent) and demonstrated the reliability of long continuous operation. [Unless indicated otherwise, Nakoso Power Plant, Joban Joint Power Co., Ltd., Fukushima Prefecture, Japan]
Previously referred to as the "black diamond" in Japan, coal was a vital component of the nation's industrial development. Although its role as a primary source of energy was usurped by oil after World War II, the oil shocks starting in the 1970s lead to coal's reemergence. Now used as industrial fuel and power generation fuel, it has become an important energy source and provides about 40 percent of the world's power.
Compared to oil and natural gas, coal has plentiful reserves, with coal fields evenly distributed around the world. Extremely economical and with a stable supply available, coal is therefore indispensable to the achievement of energy security by resource-poor Japan.
Since the Great East Japan Earthquake, demand for thermal power generation has increased. However, traditional coal-fired thermal power plants are relatively inefficient at converting thermal energy to electrical energy, because they use only the steam produced in order to generate the power to rotate the plant's turbines. Coal also has a harmful effect on global warming because it releases more CO2 emissions than other fossil fuels. In order to achieve "3E (Note) sustainability," Japan must increase power plant efficiency, while minimizing the nation's environmental load, and develop "clean coal technology" that makes smart use of coal.
Integrated coal Gasification Combined Cycle (IGCC) is a coal-based power generation technology that achieves the twin objectives of reduced CO2 emissions and increased efficiency by "gasifying" the coal and then using a gas turbine and a steam turbine in a two-stage generation process.
MHI has been researching and developing this technology since the 1980s. It has accumulated numerous proprietary technologies and demonstrated their reliability primarily with test operations at an enormous IGCC demonstration plant. The demonstration plant quite successfully finished the test operations, satisfying all targets set. With its capabilities highly evaluated through the series of test operations, the decision was made to convert it to a commercial plant owned by a utility company and to commence commercial operations in June 2013. This marks the long-awaited practical application of a pioneering technology that will open a new era for the effective use of coal.
The IGCC plant first roasts the coal in a gasifier at a high temperature in order to create inflammable gas. This gas is used to drive the gas turbine. The heat discharged from the gas turbine produces steam, which is then used to rotate a steam turbine. The coal gasification and combined cycle of two-stage power generation are the main characteristics of IGCC technology.
Prompted by the oil shocks, MHI began its R&D of coal gasification in 1983.
It gathered researchers and designers from across different divisions, built its own demonstration facility, and cultivated its original and advanced technological expertise.
Among these is the "air-blown" technology that uses air as the oxidizer in gasification.
While all other companies have adopted oxygen-blown gasification, MHI is the only company in the world to successfully commercialize "air-blown" technology.
This achievement has dramatically increased the plant's thermal efficiency.
The plant also distills MHI's numerous progressive technologies, such as "two-stage dry feed" for sending the coal to the gasifier in a stream of nitrogen with high concentration of pulverized coal powder and the expansion of the types of coal that can be used.
Coal storage yard where coal imported from around the world is collected. Low-grade coal (lignite) with a very high water content (more than 50 percent of its mass) can also be used as fuel by MHI's gasification technology.
This coal pulverizer smashes coal into minute particles smaller than 0.1 millimeter (Photo A). Pulverized coal has a larger surface area, enabling more efficient burning (Photo B).
C, D: The gasifier creates fuel gas called "syngas" from coal. Coal particles and air are blown into the gasifier, which then emits the coal syngas. The heat discharged from this process is converted into steam using a heat exchanger and used to generate power for a second time with a steam turbine. E: The burnt coal ash melts and falls into water at the bottom of the gasifier, where it is cooled rapidly into a glassy solid before being discharged.
MHI has committed every possible technology towards the pursuit of the IGCC plant's efficiency. As well as combining gas and steam turbines with a highly efficient energy-converting gasifier, MHI also makes use of the discharged heat to avoid waste. This mechanism delivers 10-15 percent better thermal efficiency than a state-of-the-art coal-fired conventional thermal power plant (ultra-supercritical coal-fired thermal power plant: USC). Because it can provide the same amount of power as a USC but using less fuel, it also cuts CO2 emissions by about 10-15 percent. This puts it on a par with oil-fired thermal power plants in terms of emissions. Moreover, the coal ash generated by gasification is discharged as glassy slag (Note), thereby reducing the required capacity of the ash disposal area as well as ash handling facilities. Environmental impact is also lowered by the reduction of emissions and discharged water that cause air pollution and sea water warming, such as SOX, NOX, particulate matter and wasted hot water. IGCC is therefore widely expected to support a sustainable future by achieving energy and cost savings with high thermal efficiency.
The glassy slag is temporarily stored in a slag hopper.
The water-insoluble "no-leaching" glassy slag can be used as a high quality material for mixtures with cement and asphalt.
The IGCC plant is a complex system that combines a gasifier, a gas turbine, a steam turbine and other interconnected equipment. It is a testimony to MHI's advanced design and engineering skills that the plant succeeds in harnessing them together into an efficient and reliable working unit. Within just a year of its start, the Nakoso demonstration plant had racked up 2,238 hours of continuous operation. This unparalleled achievement owes its speedy progress to the smooth interaction of the plant's various equipment. IGCC is expected to spawn new technologies in the future. There is a real prospect of a MHI power plant achieving thermal efficiency of over 65 percent when it launches the J-Series gas turbine that delivers world-high levels of efficiency and implements its triple-combined cycle power plant (Integrated coal Gasification Fuel cell Combined cycle : IGFC) that uses Solid Oxide Fuel Cells (SOFC). MHI has pioneered IGCC, the core technology for next generation use. It now intends to develop next generation power plant systems that deliver even higher efficiency with lower environmental impact. The paradigm shift created by the company's innovative and original technological capabilities will hopefully open the door to a new energy era and beyond.