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Liaoning looks to lift standards in magnesia processing

Government incentives and academic cooperation have spawned a number of promising new environmentally sensitive projects in the capital of China’s magnesia industry, Albert Li, IM Correspondent, finds.

Xinwei Environmental Protection Technology Co., a subsidiary of Chinese industrial conglomerate Fenghua Industrial Group based in Dashiqiao, Liaoning province, may have made a significant breakthrough in deadburned magnesia (DBM) production.

In June this year, the company produced its first DBM using environmentally-friendly, self-regulating digital technology. According to the company, it uses 20% less coal than traditional DBM production technology and yield is 20% higher, while direct emissions are practically zero.

Xinwei’s project was part of the first batch of projects to be funded by China’s Ministry of Science and Technology under the country’s 12th five-year plan for 2010-2015. Its technology took five years to develop, with the help of engineers from Liaoning University of Technology, Northeastern University, Wuhan University of Technology and Beijing University.

Xinwei and its partners have constructed a prototype production line, with four large standing kilns, each with a DBM capacity of 80,000 tpa. The production line cost Chinese renminbi (Rmb) 97m ($14.4m*) to build, but its output is expected to have a market value of Rmb 300m ($44.6m).

Although Xinwei Environmental Protection Technology Co. has worked to produce DBM using less coal than traditional production, other companies in the area are still producing large amounts of air pollution, as demonstrated in the above image, taken during a visit to a suburb of Dashiqiao.

Liaoning magnesia
Liaoning province is the centre of China’s magnesia industry. Anshan, the province’s third largest city in central Liaoning, has 148 kilns with 2m tpa DBM capacity, although recently output has been around 1.3m tpa.

Anshan’s DBM kilns are fed with magnesite ore from Liaoning’s mining areas of Dashiqiao and Haicheng.
According to Weishun Sun, an engineer at Liaoning province’s Anshan Industrial Research Institute, DBM in China is typically made using standing kilns which have high energy consumption and produce large amounts of waste gas.

Newer DBM kilns tend to be rotary models, which are more energy efficient with a higher output of DBM per unit of energy consumed. They also have higher levels of automation and can be equipped with dust collectors, desulphurisation and denitrification technology to reduce pollution.

While traditional DBM kilns are around 20 metres high and six-10 metres in diameter, Xinwei’s kilns are 47.5 metres high with an outer diameter of nine metres and inner diameter of three metres.

«The kilns are sealed and have built-in dust collectors, which reduces airborne emissions,» the company told IM. «We also use digital systems to measure out and combine the raw materials, which is much more efficient and improves the quality of the final product.»

Xinwei’s digital control of raw materials and the taller, slimmer design of its kilns reduce the amount of coal needed to heat them. It takes 150-180kg coal to heat two tonnes of magnesite ore, compared to 240kg of coal to heat 2.4 tonnes of ore in traditional DBM kilns.

Xinwei’s kilns are fitted with large fans which rapidly reduce the temperature of the DBM from 1,550-1,600 ° C in the burning part of the kiln to 180°C in the cooling section.

Other magnesia technology projects

The Chinese government, which is trying to reduce pollution and increase the quality of finished materials produced from Liaoning’s magnesia industry, hopes that Xinwei can provide a model for other magnesia companies to follow.

One of the main objectives has been to encourage magnesia producers to switch from using coal to natural gas to heat their kilns, but so far the industry has been slow to upgrade their power supply.

Some companies have however invested in modernising their manufacturing technology, in the hope of currying favour with provincial and central governments.

Anshan-based Houying Group, for example, has spent Rmb 1.8m ($267,000) since 2011 on developing a caustic calcined magnesia (CCM) gas suspension calciner. The company has constructed a plant capable of processing 2m tpa magnesite ore to produce 800,000 tpa CCM and 200,000 tpa special magnesia, using a low temperature calcination process run on natural gas.

Houying says that its low-temperature technology allows it to more accurately control the heating of the ore and running the kiln on natural gas means that carbon dioxide emissions are considerably less than they would be if the plant was run on coal.

The main drawback is that the process costs Rmb 150-200/tonne ($22-30/tonne) more than traditional CCM production, making the end products more expensive.

Haicheng Demei Environmental Protection Technology Co. has spent Rmb 90m ($13,4m) since 2014 on developing a low-grade magnesite processing project. If successful, it is hoped that Demei’s technology will offer a solution to the 300m tonnes of magnesite tailings piled in waste dumps in Haicheng by recycling them into usable materials.

The company uses flotation technology to sort the magnesite waste and its production line is capable of producing 400,000 tpa magnesium sulphate heptahydrate, 200,000 tpa magnesium sulphate monohydrate, and 170,000 tpa high-purity magnesia.

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