chinadialogue: In China, coal is the dominant energy source and the majority of this coal is used directly for burning. What serious environmental problems are caused by burning coal?
Weidou Ni: The distinguishing characteristics of China’s natural energy resources are abundant coal, scarce oil and a little gas, so in terms of primary energy production and consumption, coal has always held a dominant position. In 2005, China’s standard coal consumption reached 2.22 billion tonnes, standing at almost 70% of total energy consumption. In the use of this coal, 80% is directly for burning. Coal burned by coal-fired power plants accounts for over 50% of this. Over 70% of power plants on China’s electricity grid are coal-fired, while hydro, nuclear and other sources of power for electricity production account for no more than 30% of the total.
When coal burns, apart from producing a large amount of smoke and dust, it can also release the harmful substances carbon monoxide, carbon dioxide, sulphur oxide, nitrogen oxide, hydrocarbon organic matter and so forth. If there are no controls on these pollutants, they will have significant damaging effects on humans’ health and environment.
Carbon dioxide is universally acknowledged to be a greenhouse gas, and reducing CO2 emissions has the world’s attention. China’s carbon dioxide emissions are the second highest in the world right now, and coal is the main source of this.
Another pollutant from coal, sulfur dioxide, is the main culprit causing acid rain and, at present, the sulfur dioxide produced from burning coal accounts for more than 90% of total national sulfur dioxide emissions in China, the country with the highest such emissions in the world.
chinadialogue: Which methods can effectively remove the harmful pollutants produced from coal burning?
Ni: Reduction of carbon dioxide emissions is currently based on adopting clean coal technology and increasing the efficiency of power generation. At present, the mainstream technology for increasing the efficiency of burning coal is supercritical and ultra-supercritical power generation. In simple terms, “supercritical” is using a coal-fired boiler to heat water so that it evaporates, generating steam pressure as high as the critical pressure parameter. The optimum or highly efficient super-critical parameter is the “ultra-super-critical” point.
To tackle the issue of reducing sulphur dioxide, China has already launched comprehensive efforts for sulphur removal in coal-fired power generation. Up to the end of 2005, thermal-electric sulphur-removing systems with a capacity in excess of 200 million kilowatts of power were built nationally, making up approximately 20% of the total installed capacity at thermal power plants, and forming over 2 million tonnes of sulphur-removal capability.
However, due to the short time in which a large number of sulphur-removing facilities were constructed, management of safety and supervision was not to the required standards -- leading to a quality of sulphur-removal engineering which struggles to provide a guarantee of efficacy. After construction, many of the sulphur-removing systems were unable to operate normally, efficiency was low, there was a high occurrence of breakdowns, and the desired sulphur-removal results were not attained.
We need to find a more effective method for clean use of coal. Presently, coal gasification technology is seen as the cleanest method of coal transformation. It can be considered as the foundation for the future of clean-coal technology.
chinadialogue: What is coal gasification? Can all the environmental problems caused by burning coal be completely avoided by coal gasification?
Ni: Coal gasification technology can reduce the environmental impacts from the coal-use process to the lowest levels. Coal gasification is a thermochemical process, which uses coal or petroleum coke for raw material, and oxygen and steam for the gasification medium. At a high temperature, by a partial oxidation reaction, the raw material is transformed from a solid fuel into a gaseous fuel (main components: carbon monoxide and hydrogen).
This coal gasification technique is not new technology. It has long been employed widely in chemical engineering -- in ammonia synthesis and methanol production – so it is relatively well developed. In the wake of testing and approval of the concept of an integrated gasification combined cycle (IGCC) and its commercialisation, the use of the synthesised gas gained through coal gasification becomes one kind of clean-coal power-generating technology.
The reason why it is clean is because the synthesised gas -- which is made during gasification and contains sulphur components -- can be passed through purification technology, which removes ash and the majority of the sulphur oxides. This technique of removing the sulphur prior to burning is easier and more effective than removing sulphur dioxide from the coal smoke after it has burnt. Following from this, the use of coal gasification unites power generation and chemical engineering to form a system of multi-generation.
chinadialogue: How did coal gasification come to be the core ofthe multi-generation energy system?What are the advantages of establishing this kind of a system?
Ni: This multi-generation energy system from the coal-gasification process emerged from both the perspectives of environmental pollution and of finding an improved solution to the problem of liquid-fuel shortage. To briefly explain, it uses coal-gasification technology to change coal into a synthesis gas. After purification, this synthesised gas can be used for chemical-engineering product synthesis -- for example, methanol and ether, which are both very good liquid-fuel substitutes -- and power generation.
This kind of system of combined power-generation and chemical engineering can be used in achieving the optimal use of energy flow and matter flow, and in comparison to individual production, it can reduce energy consumption, as well as being able to achieve clean-coal power generation. And where it is needed, it can also bring about reductions in carbon-dioxide emissions.
In the long run, mankind must integrate the reduction of carbon dioxide into the energy process, and the multi-generation system provides very favourable conditions for doing this. It is much easier than extracting carbon dioxide from the smoke of a coal-burning power station. To sum up, it optimally brings together the manufacturing processes of many kinds of products. And this has striking benefits for basic investment, unit cost of product, pollution discharge (sulphur, mercury, particulate matter) and so forth, compared to the separate production of these related products.
chinadialogue: Is the technology for this multi-generation system well developed? How can it be brought into widespread implementation? Where do the current obstacles lie?
Ni: The technology that constitutes the large part of the multi-generation energy system is well developed. As long as each sector in China -- coal, chemical engineering, power generation -- breaks down the sector boundaries, to join forces and work together, and to increase international partnerships, then within three to five years it would be possible to establish a large-scale, pilot multi-generation energy installation, while having a significant number in use by the year 2020.
Presently, the multi-generation energy system has already got the nation’s attention. In China’s National High-Technology Research and Development Plan (863 program) -- from the most recent round of public announcements -- multi-generation systems and pilot engineering-project research have been linked together. Evidently, China will be creating an engineering demonstration project for the multi-generation system.
These multi-generation systems have exceptional potential for raising the efficiency of energy use and reducing environmental pollution -- so it would not be a mistake for a generation of people to engage in researching this.
chinadialogue: Currently, the shortage of liquid fuel for cars is becoming more serious day by day. Could the multi-generation system be used as an energy supply for cars?
Ni: Methanol, dimethyl ether and such are produced in the multi-generation energy system, and these can serve as oil-substitute products -- so this system could alleviate the nation’s oil shortage.
For example, a mix of methanol and petrol can be adjusted to different proportions of methanol, and 100% methanol can even be used as fuel for specially manufactured cars. In comparison to petrol and other traditional liquid fuels, methanol liquid fuel possesses some remarkable, differentiating features. It comes from many raw materials, has plentiful sources, burns completely and produces clean exhaust, while dimethyl ether is a good substitute for diesel. It can be seen from the burning process that, compared to diesel, it features slightly higher efficiency, less pollution and less noise. It now only needs improvements made to the oil-burning system.
Currently, colleges and universities in China -- for instance, Shanghai Jiaotong University and Xi’an Jiaotong University -- have research under way into the use of methanol and dimethyl ether. This includes research into problems such as friction damage caused to spare parts of fuel-injection systems, precise control of fuel-injection timing and the effects of sealing performance. The results of the research already have been put into use, and Shanghai is to have 10 to15 dimethyl ether-powered public buses in pilot operation.
Home page photo by LHOON
Weidou Ni is a professor of thermal engineering, and was formerly vice president at Tsinghua University. He is a member of the Chinese Academy of Engineering and vice chairman of the Beijing Association for Science and Technology. Ni is also a leader of the energy strategy and technology team at the China Council for International Cooperation on Environment and Devleopment.