Optimal HoSt Combustion Technology

A flexible process and optimal combustion is realised through intelligent configuration of the furnace and the temperature control system in various combustion zones. This is achieved by:

  • Applying grate zones with independent control of primary air intake and recirculating flue gasses, allowing the temperature in each grate zone to be individually controlled.
  • A robust moving floor, chain conveyor and feed-in system suitable for various biomass fuels with particle size up to 15 cm.
  • Gasifying the fuel on the grate. The flammable gas is combusted above the fuel bed in three stages:

1. Just above the grate by injecting primary air under the grate.

2. Further above the grate by injecting secondary air. Flue gasses are injected in order to control the temperature.

3. In the venturi – a highly turbulent zone – by adding tertiary air. In this way the combustion temperature can raise up to 1000 °C so that complete combustion occurs with very low CxHy, CO and NOx emissions.

HoSt has realised multiple biomass and waste combined heat and power plants in both the Netherlands and abroad. A complete overview of our projects is available here.

Fuel flexibility

Due to the zone-controlled combustion process the temperature of the grate is kept low and the temperature in the second combustion phase is maintained at a higher temperature. The low grate temperature allows a greater variety of biomass fuels with low as melting point to be processed. This might include wood (with leaf), compost, straw, chaff and similar biomass waste products.

High efficiency with low emissions

The zone-controlled combustion process results in a high efficiency, complete combustion, with low emissions of CxHy, CO and NOx. The high efficiency is achieved by minimising stack losses and keeping the flue gas flow low. The low flue gas flow is achieved through optimal combustion that resulting in O2 concentrations of 3.5% to 5% in the flue gasses.

Minimal maintenance costs

The furnace concept has a positive effect on maintenance, in particular:

  • Long grate lifetime due to low grate temperatures.
  • Ash disposal system is insensitive to failure, due to a robust and wet chain conveyor. This system is robust and relatively insensitive to rocks, ash agglomerates and other contaminants that may be present in the fuel.
  • Fully automated ash disposal system. Ashes at the end of the grate, ash falling through the grate and ash from the first phase flue gas cleaning (multi-cyclone) are collected in the wet ash disposal system.
  • The wet ash disposal system minimises the dust forming in the boiler building. This has a positive effect on the life time of control systems and electric drives.

High availability

HoSt biomass plants have demonstrated practical availabilities between 92% and 94%, often with an availability of in excess of 8200 operating hours per year. This high availability is achieved by:

  • A robust design from moving floor and fuel conveyance through to the feedin system. Possible contaminations do not lead to downtime.
  • A grate with low maintenance requirements due to low grate temperatures.
  • An absence of horizontal combustion chambers results in no additional cleaning stops due to dust accumulation, as opposed to boilers with horizontal labyrinths where it is necessary.
  • Optimizing the boiler for minimum fouling and by equipping the boiler with an automatic cleaning system.


Interested in what we can offer? Or interested in visiting one of our projects? For example the wood-fired bioenergy plant in Beetgum, the bio-CHP in Strijp or in Meerhoven? Or do you need more information about our biomass boilers and waste boilers? Contact us. We would be glad to assist you and help you in making the best choice.

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