Turning waste into green electricity

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Monday 21 December 2020 11:14 AM

Turning waste into green electricity

In the Chinese city of Shenzhen, using landfill gas three MTU gensets are generating almost 6 thousand kilowatts of electrical power.

China's Silicon Valley

The city of Shenzen is also called the Silicon Valley of China. From 30,000 inhabitants in the early 1970s, the southern Chinese city has grown to more than ten million, with glittering skyscrapers, a modern transportation system and world-class shops. New factories and start-ups open almost daily, driving the boom. But this growth also brings problems with it: energy demand is rising, and the environment is being polluted.

Power generators from Rolls-Royce now help to solve these problems. Landfill gas is produced at the many waste disposal sites and our gensets take this and produce electricity.

The big challenge

Landfill gas is a waste product that is relatively easy to obtain.

Bacteria decompose the organic part of the waste and thereby produce landfill gas. It contains the flammable methane that gas engines run on. However, depending on the type of waste that decomposes, the composition of landfill gas is different and so is the methane content. On average, between 35 and 60 percent of landfill gas consists of methane, the rest is carbon dioxide. And the amount of methane has a great influence on the performance of the engine. If the methane number of the gas is too low, the engines begin to knock: then parts of the compressed gas-air mixture explode even before it has been fully ignited by the spark of the spark plug and the engine's performance drops.

So far, MTU's gensets have proven themselves under very difficult conditions. The units operate in the most humid and hot environment in China, and the site ventilation conditions are very poor.

Xuming, Head of the New Energy department at Micropower, the operator of the plant Shenzhen Shengshi Energy Co, Ltd. based in Longgang District, Shenzhen City.

Using landfill gas that would be generated anyway

In recent years, Shenzhen Shengshi Energy Co, Ltd has had twelve landfill biogas power plants with a total capacity of 120 megawatts built, and six more are currently under construction. The company feeds the electricity into the public grid. This is because landfill gas is still a large market in China - unlike in large parts of Europe. It is true that the Chinese government is also increasingly focusing on separating and recycling waste.

But 70 percent of municipal waste in China is still being disposed of in landfills. "Making use of these gases, which are in any case produced during the fermentation of this waste, is a great benefit for China," says Darren Ding. It's a win in two respects: in addition to the economic gain, the environment also benefits by not letting the landfill gas escape uncontrolled or being flared. So Darren and his colleagues are working to ensure that more landfill gas power plants in China are equipped with MTU cogeneration units.

How landfill gas is produced

During degradation processes, gaseous metabolic products are excreted in landfills. Microorganisms that decompose the waste release methane and carbon dioxide under certain oxygen and temperature conditions. At the end of the biochemical degradation process, a water-saturated gas mixture is produced, which is called landfill gas.