The blending of coal is the key to whether a coal-fired power plant obtains reasonable output while encountering slagging and fouling issues, or whether it runs consistently at capacity with minimal down-time, the IEA said.

“Old mines close and new mines appear,” it said.

“Operators do not have the luxury of being able to afford, or even source, their favourite coal for the lifetime of their plant. Blending allows big operators to make the most of the hundreds of coals available on the international market place. But it also allows small plants to make the most of what they have available.”

Blending processes can be controlled in real-time with online sampling and analysis systems, according to the IEA.

Coal deliveries by train or ship can be co-ordinated by advanced management systems so that silos and stockpiles deliver the blends demanded by the customer.

“Coal blending is a complex issue. But most plants manage to adjust to coal blending requirements through a combination of outside expertise, trial and error, and judgments made by a qualified on‐site expert,” the IEA said.

The flow of internationally traded coal gives an idea of just how much coal is transported between continents and how far it may travel, according to the IEA.

As demand for coal continues, new mines are developed and new infrastructure is created to make this coal available to the international market. Coal users now have more opportunity to pick and choose coals than ever before.

Blending allows plants to take advantage of the different coals available to them. Many modern plants in southeast Asia are designed to burn up to 100 different coal types of various quantities and ranks and will blend coals before use.