Generally speaking, the coal of power plant is low-grade, high-ash (the low content of fixed carbon) and the effect of direct gasification is bad.

一般说来，电站煤质的品位低、灰含量高(低的固定碳含量)，直接气化效果很差。

youdao

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The volcano spurted clouds of steam and ash high into the air.

火山把团团热气和灰尘喷向高空。

《牛津词典》

Usually, the prevailing south-westerly wind would take the ash cloud away from Europe and over the polar region, but a high-pressure area is bringing it over Europe, where it is sitting and barely moving as the ash spreads.

BBC: Volcano cloud threatens Formula 1 preparations

Both BA and KLM, after all, had direct experience of what flying through volcanic ash can do to a high-bypass turbofan jet engine.

ECONOMIST: The effect on business and leisure

Ryanair said the "red zone" over Scottish airspace where ash has been classified "high-density" was invented by the Met Office and the Civil Aviation Authority (CAA).

BBC: NI flights cancelled as ash cloud approaches