Any type of fuel can be used in any boiler if it is designed for the fuel. The difficulty that always arises is fouling of heat transfer surfaces. This tends to make water tube boilers more suitable for high fouling fuels / gases.

The main reason for selecting a water tube boilers is usually pressure and superheat required. For smaller boilers at low pressure the fire-tube boilers is more common as they are inherently less expensive than water tube boilers..

I will make a small addition/explanation to the above:

(1) the water side of a fire tube boiler is the shell and this is significantly larger than the tubes in a water tube boiler. A large shell as design pressure increases becomes very thick and there becomes an economic upper limit to the shell thickness.

(2) At low steam pressures the steam as opposed to the water specific volume is large and steam separation is easier to arrange. As the design pressure rises a given mass of steam occupies a smaller volume and the switch to the steam drum required with a water tube boiler becomes feasible

(3) you can have a small superheater with a firetube boiler.

(4) water tube boilers have more flexibility of configuration than firetube ones hence combustion volume can be more easily arranged

(5) water tube boilers can run to supercritical pressures but these do not need a steam drum

Stephen

Jack Broughton Why is water tube boiler suitable for high fouling fuels ? Could you Please clarify.

A water tube boiler can be designed with large tube clearances and low gas velocities. The large tube spacings make deposits have less effect and the low velocities reduce erosion dramatically. Additionally, if a gas has a large solids loading, erosion shields can be fitted around the front of tubes.

Having said this, locomotive boilers burn coal happily and many fire-tube boilers operate with dirty fuels. However, these boilers need more frequent cleaning than water tube boilers. Ultimately, selection of boiler type is a matter of "horses for courses".