Water Pipe Boiler

In principle there are two kinds of steam boilers available:

  • A cylindrical flame tube boiler.  The flue gasses flow through the pipes heating the water flowing outside of the pipes.
  • A water tube boiler, the water/steam flows through the pipes (water cooled membrane walls and convection pipe bundles) heated by the fluegasses flowing outside of the pipes.

The water tube boiler has some serious advantages over the flame tube boiler: the pressure of a cylindrical flame tube boiler is limited to around 25 – 30 bara, and thereby limits the efficiency of a steam cycle. Furthermore, a water tube boiler is far less sensitive to fouling when using biomass fuels. In the most severe commercial applications like waste incinerators, a water tube boiler is the boiler of choice. If fouling does take place, cleaning of the boiler can be accomplished relatively easy by conventional steam soot blowers.

A water tube boiler is normally applied in big capacity plants and can not be bought on the market for the relative small scale of biomass plants in the range 1 – 5  MWe.  Because of this fact HoSt has developed its own water tube boiler, to suit the need of smaller biomass plants. The boiler has been proven in a commercial wood fired CHP plant built by HoSt, with a availability of the plant of more than 92%.

The investment cost of a water tube boiler is higher than the cost of a flame tube boiler. However if a high efficiency and reliability in a project is required, especially for biomass/waste fuels with known severe fouling behaviour, the HoSt water tube boiler will be the best choice for the project.

In a gasifier project the HoSt syngas burner will be placed on top of the boiler in a vertical position. Cooling of the flue gasses will take place in the first vertical pass by radiation, heating the water/steam mixture in the membrane walls. In the second vertical pass (flue gasses flowing from the bottom to the top)  water/steam pipe bundles are placed to transfer the heat by convection. The pipe bundles will be cleaned by steam soot blowers.

Waterpipe Boiler HoSt BV