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.
*Conversions made August 2017