The eye-popping economic growth of China, contrary to popular perception, is having some positive impact on the environment. Power companies are closing down inefficient coal plants almost as rapidly as a new breed of ultrasupercritical units are being ordered. PEi visited one such new facility – the world’s largest – the 4 x 1000 MW Yuhuan plant in Zhejiang province, 500 km south of Shanghai.

By: Tim Probert, Associate Editor

If it can be said that the US is addicted to crude oil, then China can be said to be addicted to coal. Around 80 per cent of China’s total electricity production comes from coal, and the country has colossal reserves at its disposal. However, the ensuing environmental damage, not least the impact on the health of Chinese citizens and those of neighbouring countries, is painfully obvious. In northern China, cities like Beijing and Shenyang have some of the highest readings in the world for total suspended particulates and sulphur dioxide, with coal burning being a major source of this. In southern China, large areas have growing acid rain problems.

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Beijing is under severe pressure from the international community to embrace cleaner coal, but while there has been plenty of lip service paid to its ecological responsibility, the Communist Party has made few moves to regulate greenhouse gas emissions. Central government, under its latest Five Year Plan, has set targets to reduce overall energy consumption at a local level, but there are no specific regulations to limit sulphur dioxide or nitrogen dioxide emissions, for example. Moreover, Beijing’s diktats for local regulations can be altered by the provincial governments. Ecological responsibility has simply not been particularly high on Chinese power plant owners’ lists of priorities. Economic growth has put tremendous strain on power supplies, and so power plants have been mostly concerned with maximizing output. Tellingly, flue gas desulphurization units are unusual in China, even at large power plants, and it is not uncommon for units to be installed and then turned off to gain ‘efficiency’.

However, matters have come to a head. China has faced its most severe power shortage ever in recent weeks. Some plants have struggled to secure increasingly costly coal, while others have shut down capacity rather than rack up losses by selling electricity at low rates. Brownouts have hit at least 13 provinces, and peak nationwide demand has outstripped supply by nearly 70 GW, or the equivalent of most of the UK’s generating capacity. So, faced with the prospect of importing more coal at record high prices, coal-hungry, highly polluting, subcritical coal fired power plants are out; efficient supercritical and ultrasupercritical coal fired units are in. Under Beijing’s 11th Five Year Plan, some 50 GW of inefficient capacity is set to be purged by 2010 as China seeks to cut per-unit energy consumption by 20 per cent and – perhaps a more pressing requirement – make its coal supplies go further.

East and West join forces

This efficiency drive has meant that cutting-edge coal fired units are in great demand in cash-rich China. Just ask Siemens, which, in tandem with Shanghai Electric Group (SEG), has secured orders for 24 ultrasupercritical units of 1000 MW each in recent months. Siemens has a strong presence in China. The German conglomerate, which secured its first Chinese order way back in 1872 to deliver the country’s first pointer telegraph, employs more than 42 000 people in the world’s most populous nation.

Perhaps Siemens’ best-known project in China is the Shanghai Maglev train, which whizzes passengers along a 31 km route from Pudong International Airport to Longyang Road metro station in just seven minutes and 20 seconds, reaching a breathtaking top speed of 431 km per hour. But while the Maglev is certainly an impressive feat of engineering, and quite possibly the closest experience that passengers will have to the flight of an astronaut whilst being seated in a comfortable armchair, in reality it amounts to an ultra-expensive luxury, little more than a fairground attraction.

Eminently more useful – and almost as impressive – is Huaneng Power International’s (HPI’s) $2 billion, ultrasupercritical coal fired power plant in Yuhuan in Zheijiang province. Yuhuan is 500 km south of Shanghai, from where it is reached via a 45 minute flight to Hangzhou, capital of Zheijiang, and then 90 minutes connection by road, where the shiny new cars and motorcycles ubiquitous in Shanghai give way to the rusty bicycles one usually associates with China. But, surrounded by mountains on three sides and casting an imposing figure by the East China Sea on the other, the Yuhuan plant is the very model of a modern major power plant. It is also the most efficient coal fired power station in the world, and the world’s largest ultrasupercritical plant. With a capacity of 4 GW and set to generate 22 TWh a year when fully operational, it is also China’s second largest coal fired power plant.

Major step forward for Chinese coal plants

The first phase of the plant, which includes two 1000 MW generating units, was finished in December 2006. As of February 2008, three of the four 1000 MW coal fired ultrasupercritical pressure boilers have come online. Unit 4 is expected to come online later this year.

The Yuhuan coal fired plant utilises four 1000 MW capacity steam turbines built by Siemens
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The ultrasupercritical units that comprise Yuhuan represent somewhat of a great leap forward for Chinese coal fired plants, as they help to address two issues urgently facing the country: the need to increase power generation capacity in the East China grid and thus alleviate the severe capacity shortage in that region, and the need to reduce pollution. Subcritical coal plants in China typically have an efficiency of below 30 per cent. Supercritical operation of large thermal baseload power plants during the 1980s tended to use steam temperatures of 550 °C, leading to thermal efficiencies of around 40 per cent. Ultrasupercritical steam conditions use supercritical pressures of up to 300 bar (30 MPa) with 600 °C steam and reheat steam temperatures.

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With ultrasupercritical technology, a power generating unit operates under a mixture of temperatures and pressures above the critical point, at which the boundary of water’s liquid and vapour state disappears. By eliminating the transition of water into steam, the power units increase fuel efficiency, in Yuhuan’s case to an impressive 45.16 per cent. By way of comparison, the average European coal plant has an efficiency of 36 per cent.

China has strict “nationalization” rules, which stipulate that around three quarters of power plant equipment must be manufactured domestically. To comply, foreign firms usually enter into a joint venture with a Chinese company. In this case, Siemens, in conjunction with SEG, supplied the four 1000 MW ultrasupercritical steam turbines under technology transfer agreements. In effect, Siemens provides the brains: the technology for the steam turbines, the engineering, the technical services and the key components. The turbines and generators – the brawn – were manufactured by SEG. Siemens also provides ongoing technical support to the Zheijiang branch of HPI.

The turbines use a tandem, compound, four-cylinder arrangement. Steam enters the high-pressure turbine through two main steam valves, with exhaust steam being reheated and fed to a double-flow intermediate-pressure turbine. From there, it goes to two low-pressure turbines.

The Mitsubishi Heavy Industries (MHI) boilers – the first 1000 MW boilers in China – have a main steam pressure of 251 bar (25.1 MPa), a main steam temperature of 605 °C and a reheat steam temperature of 603 °C. The boilers were made and commissioned collaboratively by MHI in Japan, who provided the designs and key products, and Harbin Boiler Company (HBC) in China. Unit 4 is now under construction by MHI and HBC. The high-pressure feedwater heater uses technology from Foster Wheeler. The 1000 MW ultrasupercritical units adopt a horizontal three-zone arrangement: a desuperheating zone, a condensing zone and a drain subcooling zone.

Emerson Process Management’s Ovation control system has been implemented after the US firm won the $7 million contract to automate the plant in April 2005. The system monitors and controls the data acquisition system, modulating control system, sequence control system, furnace safeguard supervisory system and electrical control system for all major plant components. That includes the boiler, turbine, generator and balance of plant processes. HPI says that Ovation allows high levels of plant availability, reliability and environmental compliance. The system also provides a seamless interface with the most widely adopted bus standards, allowing smart device technologies to be incorporated into processes.

Saving coal, saving emissions

According to HPI, the four 1000 MW ultrasupercritical units will save 400 000 tonnes of coal equivalent per year compared with supercritical power plants. Carbon dioxide emissions will be reduced by over 500 000 tonnes, and sulphur dioxide by over 6000 tonnes.

The new units also incorporate high-efficiency dust removal and flue gas desulphurization. In fact, HPI states that the plant is overperforming in terms of coal consumption.

Testing has shown consumption to be 283.2 g per kWh against the 290.9 g as designed (Table 1). This is significantly below the national average consumption for 2006 of 367 g per kWh. Yuhuan is also leading the way in cutting sulphur dioxide emissions, which have been tested at 17.6 mg/Nm3 versus the national average of 95.3 mg/Nm3.

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To save oil consumption, the four units adopt MHI’s plasma ignition technology. During units 1 & 2’s startup, commissioning and test period, the boilers’ cold-state, oil-less ignition kicked in, saving around 10 000 tonnes of fuel oil. After the phase I units were put into production, plasma ignition also has realized zero oil consumption in cold-state startup. The units are also equipped with electrostatic precipitators with a design efficiency of 99.7 per cent.

The limestone-gypsum wet process desulphurizers are constructed concurrently, and the desulphurization rate is not less than 95 per cent. Furthermore, the boilers adopt low-nitrogen combustion technology, and the design NOX emission level is just 360 mg/Nm3.

Yuhuan is a thoroughly modern Chinese power plant in other ways besides its adopted technology and environmental responsibility. In China’s recent past, power plants were not just places that produced electricity, they often provided a focal point for the locality, providing education as well as offering one of the easier routes to employment within the community. This is not the case at Yuhuan. Efficiency is the name of the game, and this applies to manpower just as much as coal consumption.

HPI, China’s largest independent power producer, is keen to stress the efficiency of its manpower as well its coal firing power. The Chinese are fond of slogans, and HPI is no different. In this case, the maxim is to employ people who are “experts in one thing and good at several” and to have such personnel on duty at all times. Its new 1200 MW combined cycle gas fired power plant in Shanghai – also built with Siemens’ technology – boasts a workforce of just 42, which HPI says is the lowest manpower-to-megawatt ratio in the world. However, the workforce could also be the least active in the world. When the author paid a visit to the plant, completed in July 2007, state-imposed natural gas rationing meant that none of the three 400 MW units were generating electricity.

The Yuhuan power plant is not just a showcase power plant for China but for the world. It may take some time, but with the help of technology transfers from the likes of Siemens and Mitsubishi and the prospect of carbon capture in the years ahead, the prospect of China embracing clean coal does not seem as fanciful as perhaps it once was.