Engineering news
MIT Researchers in the US have designed a hybrid coal power plant concept they claim could double the fuel-to-electricity efficiency of conventional coal plants and halve their carbon emissions.
The system combines coal gasification and fuel cell technology. Coal gasification is used to extract burnable gaseous fuel from pulverised coal, rather than burning the coal itself. Fuel cells are then used to produce electricity from the gaseous fuel by passing it through a battery-like system, where the fuel reacts electrochemically with oxygen from the air.
According to Katherine Ong, the MIT researcher who has proposed the concept, the key advantage is that because both processes operate at high temperatures of 800 degrees Celsius or more, combining them in a single plant would allow them to exchange heat with minimal energy losses.
The fuel cell would also generate enough heat to sustain the gasification part of the process. Usually, this heat is provided by burning some of the coal
Additionally, computer simulations conducted by the research team have revealed that the use of steam instead of CO2 to react with the coal during gasification, could increase the hybrid system’s power output by up to three times.
The next step is to build a pilot-scale plant to measure the performance of the hybrid system in real-world conditions. “This system requires no new technologies” Ong said, “it’s just a matter of coupling these existing technologies together well.”
“If we’re going to cut down on carbon dioxide emissions in the near term, the only way to realistically do that is to increase the efficiency of our fossil fuel plants,”.
Hybrid process
First, the coal is pulverised to a powder, which is then heated in a flow of hot steam. The heat leads to chemical reactions that release gases from the coal particles — mainly carbon monoxide and hydrogen, both of which can produce electricity in a solid oxide fuel cell.
In the combined system, these gases would then be piped from the gasifier to a separate fuel cell stack, or ultimately, the fuel cell system could be installed in the same chamber as the gasifier so that the hot gas flows straight into the cell. In the fuel cell, a membrane separates the carbon monoxide and hydrogen from the oxygen, promoting an electrochemical reaction that generates electricity without burning the fuel.
Because there is no burning involved, the system produces less ash and other air pollutants than would be generated by combustion. It does produce carbon dioxide, but this is in a pure, uncontaminated stream and not mixed with air as in a conventional coal-burning plant. That would make it much easier to carry out carbon capture and sequestration (CCS) — that is, capturing the output gas and burying it underground or disposing of it some other way — to eliminate or drastically reduce the greenhouse gas emissions. In conventional plants, nitrogen from the air must be removed from the stream of gas in order to carry out CCS.
Source: MIT