Complex sentence: Huntly coal mine is New Zealand's largest producer of coal, producing over 10,000 tonnes a day, the major New Zealand clients are the power station, and New Zealand steel at Glenbrook.
Split into simpler sentences: Huntly coal mine is New Zealand's largest producer of coal, producing over 10,000 tonnes a day. The major New Zealand clients are the power station, and the New Zealand Steel mill at Glenbrook.