Although coal's share of China's energy budget is supposed to drop to 52 percent by 2030 in favour of renewables, nuclear power, and natural gas, the amount of coal burned — not only for electricity generation, but also for the production of raw materials for industry —is expected to continue increasing, according to Siemens projections.
Gasifying powdered coal at high temperature
As a leader in efficient, low-emission technologies, Siemens helps to develop and commercialise coal gasification. It is an established technology based on a simple principle: powdered coal – in other words, almost pure carbon – is gasified at a high temperature together with oxygen. The result is a synthesis gas of hydrogen and carbon monoxide. Using water, the carbon monoxide is converted into carbon dioxide and hydrogen.
Integrated gasification combined-cycle (IGCC) plants use this process to supply high-purity hydrogen that can be mixed with natural gas in a gas turbine to produce electricity. "Here, CO2 has already been separated out, and rather than being released into the atmosphere, it could be injected into an oil field to increase its yield, for example," a Siemens engineer said, explaining:
"Electricity generation would then be almost entirely CO2-free – a goal that will be achieved by an IGCC plant under development in the USA: the Texas Clean Energy Project." That plant is expected to produce electricity and fertiliser with gas turbines supplied by Siemens, while the CO2 is injected into an oil field.
IGCC suited for generating electricity & producing chemicals
Power generation is one way to use the IGCC project, but it can also be used to produce chemicals for industrial purposes.
"It is the ideal way to use different carbon-containing fuels like coal, refinery waste, and even organic waste to produce many different materials — "basically, anything that contains carbon," said Frank Hannemann, head of Technology and Innovation at Siemens Fuel Gasification Technology GmbH in Freiberg, Germany.
"Plastics, methane (natural gas), methanol, diesel, fertilizer – there are almost no technical or chemical limits to what can be produced from coal," he suggested.
5x500 MW coal gasifier built in Ninxia
In China, most coal reserves are located in remote regions like the northern Chinese steppe where there are very few customers for electricity. Together with coal-mining company Shenhua Ninxia Coal Group, Siemens has built a coal gasification plant near the Mongolian border. The plant has an output of 5 times 500 megawatts.
For the five fuel gasifiers at the plant, Siemens is using an advanced design with a pneumatic coal conveyance system and full quench design which require less high-pressure steam to convert the carbon monoxide it generates into hydrogen, he explained, stressing "all of these features result in greater efficiency and lower CO2 emissions."
The team of Dehui Wang, Technical Manager at Siemens Corporate Technology in Beijing, supports Mr Hannemann R&G group. Using an experimental plant to study the chemical reactions that occur when hot synthesis gas is cooled, Ms Wang's team has contributed to a new type of shift process that uses water to convert carbon monoxide into carbon dioxide and hydrogen.
Developing advanced gasification processes in China
Based on Clariant's catalyst, a two-step CO-shift process is being used, with an inhibiting catalyst in the first step. The catalyst slows down the reaction, causing only a small portion of the gas to be converted in the first step. The complete reaction takes place in a second step using a state-of-the-art catalyst.
"What gives this solution an edge over other approaches is that, because the process is slowed down, it requires less steam for cooling the hot gas (which has a temperature of up to 1,400 degrees Celsius), and that makes it more efficient overall," Ms Wang pointed out.
Together with Siemens' Fuel Gasification Business Unit, she is now looking for a customer in China to demonstrate this new technology.
"The facility sets new standards for efficiency," she said but cautioned "it isn't quite as environmentally friendly as it could be." The CO2 is removed, but it is not stored underground. Shenhua Ninxia Group considers this to be too uneconomical and still releases its carbon dioxide into the air.