Switching a boiler from gas to coal: what to know first

Why factories are looking at coal again

Pipeline gas for industry is short again and RLNG is expensive. Coal reached a record 22% of Pakistan's electricity in the first nine months of the financial year as power plants made the same switch.

For a factory, coal is cheaper per unit of heat than RLNG and the supply does not depend on the gas network.

What changes with a coal boiler

A gas boiler cannot simply be fed coal. You need a boiler designed for solid fuel, with a grate or a fluidised bed, coal handling, ash removal and usually a dust collector. Some gas boilers can be converted, but often a new or second hand coal fired boiler is the practical route. Your boiler maker will tell you which applies.

You also need space to store coal under cover, and staff to fire the boiler and clear the ash.

Which coal suits which boiler

Chain grate and travelling grate boilers want sized coal with little dust, so lump or a screened size suits them best. Fluidised bed boilers take smaller sizes and can burn lower grade coal.

For most boilers we suggest Sor Range coal: around 6,500 kcal/kg, about 9% ash and the lowest sulphur of the Balochistan coals at around 3%, at about Rs 38,500 a tonne ex-Quetta. Chamalang is the next choice.

Sulphur and the boiler

Sulphur is the thing to watch. It forms acid in the flue gas that corrodes the back end of the boiler if the gas cools too much. Keep the flue gas temperature above the dew point and check your environmental approval for any sulphur limit before choosing a coal.

Questions to ask a coal supplier

Can you supply the same grade and size every week? A boiler set up for one coal runs worst when the coal keeps changing.

Will you send a lab analysis with each lot? How much do you hold in stock for the winter months? And what happens if a truck is short or wet?