Improving the efficiency of biofuel boilers: installation of a primary air heater.

PAS „Daugavpils siltumtikli“

Daugpilis, Latvia

2025

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In 2025, UAB GANDARAS ENERGOEFEKTAS implemented a project to install a primary air heater for a wood chips fired boiler.

This solution was another step towards improving the efficiency and reliability of biofuel boiler plants operated by PAS “Daugavpils siltumtīkli”.

The installation improved the combustion process, increased equipment efficiency and ensured stable operation even when burning fuel with high moisture content.

Features of wood chips fired boiler operation

Boilers that use wood chips as fuel have three main technological zones on the grate:

1. Drying zone – the fuel heats up and moisture evaporates.
2. Combustion zone – active wood combustion and heat release take place.
3. Ash formation zone – the combustion process is completed and ash is formed.

Burning the wood chips with a moisture content of 55–65%, a problem often arises: the fuel does not have time to dry completely in the first zone, which reduces the combustion zone and decreases the efficiency of the boiler.

Solution — primary air heater

To solve this problem, a primary air heater was installed, which supplies air to the drying zone with a temperature of about +90 °C and an oxygen content of up to 20%.

The heated air provides:

• more efficient drying of wood chips before combustion;
• stabilization of the combustion process;
• reduction in the formation of unburned particles and CO emissions.

Thus, the primary air heating system creates the effect of combustion zone ‘lengthening’, ensuring complete and uniform combustion even of wet fuel.

Heat source for preheating

Depending on the boiler operating mode, primary air is preheated in different ways:

• in operating mode — by recirculating a portion of the flue gases and heat from the heated district water;
• during the ignition phase, when the flue gases are still cold, — using only heat of the heated district water.

This approach ensures a quick and safe boiler start-up, stable operation at nominal parameters, and the absence of temperature fluctuations in the furnace.

Key benefits of implementing the system

• Stable combustion with fuel moisture content up to 60%.
• Increased boiler efficiency and reduced fuel consumption.
• Reduced carbon monoxide and solid particles emissions.
• Extended service life of furnace and grate equipment.
• More stable operation of automated control systems.
• Reduced dependence on fluctuations in biofuel quality.

Results and conclusions

Thanks to this solution, biofuel boilers now ensure better combustion of wood chips, stable temperature conditions and maximum efficiency even when operating with wet fuel.

The UAB GANDARAS ENERGOEFEKTAS project demonstrates that the use of modern engineering solutions allows local renewable resources to be used with maximum efficiency and provides reliable heat supply to the city's residents.