(Adds background on facilities in Dalian)

BEIJING Aug 31 (Reuters) - State-owned China National Petroleum Corp (CNPC), parent of PetroChina , has replaced the head of Dalian Petrochemical Corp, the company said on its website on Wednesday, following a second fire in the largest company plant in less than two months.

A diesel tank storing about 800 tonnes of fuel in the plant located in northeastern Liaoning province caught fire on Monday morning, and a fire on July 16 in a heat exchanger forced the shutdown of a 200,000 barrel-per-day (bpd) crude unit for six weeks.

PetroChina, which operates most of CNPC's oil and gas businesses, is restarting the crude oil unit in the 410,000-bpd oil refining plant.

CNPC said on its website that it has appointed Leng Shengjun, head of its subsidiary refinery in Daqing, as the new general manager of Dalian Petrochemical Corp.

A pipeline blast on July 16, 2010, at Dalian's oil port spilled 1,500 tonnes of oil into the sea, the government said. But environmental group Greenpeace estimated the leaks may have been as high as 60,000 tonnes.

Dalian, a city of six million people and the second-biggest city in Liaoning province, is the home of two main refineries operated by PetroChina -- Dalian Petrochemical Corp and West Pacific Petrochemical Corp (WEPEC) -- with a combined crude run capacity of 610,000 bpd.

It is also the site of privately-run Dalian Fujia Petrochemical, which earlier this month was ordered to shut down by local authorities after thousand of local residents demonstrated, demanding the relocation of the factory at the centre of a toxic spill scare.

PetroChina will also start soon a 3 million tonne-per-year import terminal for liquefied natural gas (LNG) in Dalian.

(Reporting by Jim Bai and Chen Aizhu; Editing by Ken Wills and Greg Mahlich)