Shanxi, a mid-sized province located in northen China, is one of the 34 provisional units in the country. Shanxi is the biggest coal supplier in China. [1] In 2009, Shanxi supplied about 1/4 of the total coal in China. 70% of the total electricity power in China is generated from coal, so about 17.5% of the total energy in China is from Shanxi. [1] However, tremendous pollution caused by coal industry makes Shanxi people suffer from the severely destroyed environment for years. Taiyuan, the capital of Shanxi, has become one of the cities with worst air quality in the world. Cleaning up Shanxi is not trivial. Most of the pollutions are from coal mining, transportation and coal fired power plants. This report will mainly talk about how to reduce the pollution from coal plants. That is, how to clean the process of burning coals.
In recent years, a new technology called Integrated gasification combined cycle (IGCC) has been proved to be more energy efficient and environmentally friendly. IGCC is a technology that turns coal into syngas (CO + H2) the presence of a controlled 'shortage' of air/oxygen and then removes impurities from the syngas before conbustion and attempts to turn any pollutants into re-usable byproducts, such as pure elemental sulfur. [2] It can reduce emissions of sulfur dioxide, nitrogen oxide, particulates and mercury. The outstanding CO2 capture capability also makes this technology more favored in a carbon constrained world that global warming is concerned more than ever before.
There are several advantages of IGCC that makes it stands out of all the competitive clean coal technologies. First, it emits fewer pollutants. The solid emission (ashes, particles) of IGCC has both less volume and better form compared to conventional coal plant. IGCC produces about half the solid wastes of conventional coal plants and its solid wastes have less toxic metals than fly ash from conventional coal plants.As a result, very low particulate emission levels are achieved. For example, the Wabash plant reported emissions of less than 0.012lb/106 Btu heat input, which is well below the current Federal NSPS requirement of 0.03 lb/106 Btu heat input. [3] In Shanxi, the primary pollutant is solid emission and IGCC will be able to reduce it significantly.
IGCC plants can be configured to facilitate CO2 capture. On average, IGCC plants produce CO2 at a rate of about 1.85 lb/kWh, while the conventional pulverized coal-fired power plants yield about 2 lb/kWh. [3] However, with an IGCC plant modified to produce hydrogen, a CO2 discharge rate of 1.2 lb/kWh may be able to be achieved. [3] Further more, if carbon capture function is interrelated into the system, about 90% of CO2 can be removed with a cost of 5% to 10% degradation of the overall efficiency. [4,5]
Secondly, it produces more energy with the same amount of coal. It uses a combined cycle format with a gas turbine driven by the combusted syngas, while the excess heat from the primary combustion and generation is then passed to a steam cycle to drive a steam turbine to produce additional electric power. Compared to other clean coal tech, IGCC has significantly higher efficiency of about 43% to 45%. [2] In terms of water usage, IGCC uses use 20%-50% less water than conventional coal plants and can utilize dry cooling to minimize water use. [3]
In addition, IGCC has great flexibility of polygeneration. It produces not only electric power, but also hydrogen, steam, zero-sulfur diesel, chemicals such as pure sulphur and acids.
The major concern of IGCC is its high capital and operating costs. The initial stage of investment is huge compared to conventional power plant. However, in a long term run, with the environmental cost increasing, this technology may become both economically and environmentally efficient.
Construction of the first IGCC power plant in China, Huanen Greengen IGCC power plant located in Tianjin started in 2010 with 0.3 billion US dollars invested and an expected capacity of 250 megawatt. This project will be a model to learn for Shanxi province and the clean coal in Shanxi can be achieved by applying IGCC.
In summary, IGCC technology will reduce pollution, make more electricity with the same coal, which will provide a real path toward cleaner Shanxi.
© 2010 Dong Liang. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] W. Wei, "Current Issues of China's Coal Industry: The Case of Shanxi," Proc. 15th Annual Conference of the Association for Chinese Economics Studies Australia (ACESA), October 2003.
[2] C. Descamps, C. Bouallou and M. Kanniche, "Efficiency of an Integrated Gasification Combined Cycle (IGCC) power plant including CO2 Removal," Energy 33, 874 (2008).
[3] J. M. Beer, "High Efficiency Electric Power Generation: The Environmental Role," Prog. Energy Combustion Sci. 121, 107 (2007).
[4] P. Chiesa and S. Consonni, "Shift Reactors and Physical Absorption for Low CO2 Emission IGCCs," ASME J. Eng. Gas Turbines Power 121, 295 (1999).
[5] R. Pruschek R et al, "Combined Cycle Power Plant with Integrated Coal Casification, CO shift and CO2 Washing," Energy Conversion and Management 36, 797 (1995).