Biomass heating system with optimized flue gas treatment

A biomass heating system for combusting fuel in the form of pellets and/or wood chips, comprising:

• a boiler with a combustion device;
• a heat exchanger with an inlet and an outlet;
• wherein the combustion device possesses a combustion chamber having a primary combustion zone and a secondary combustion zone arranged downstream thereof;
• wherein the secondary combustion zone of the combustion chamber is fluidically connected to the inlet of the heat exchanger;
• and
• wherein the primary combustion zone is laterally enclosed by a plurality of combustion chamber bricks wherein, the biomass heating system possesses the following:
• a recirculation device for recirculating flue gas generated by the combustion of the fuel in the combustion device wherein the recirculation device possesses the following:
• a recirculation inlet that is provided downstream of the outlet of the heat exchanger and fluidly connected to the outlet of the heat exchanger;
• a primary air duct for the supply of primary air;
• a primary mixing unit with a primary mixing chamber and a primary mixing duct,
• wherein the primary mixing chamber is provided downstream of the recirculation inlet and the primary air duct and fluidly connected with both of the recirculation inlet and the primary air duct;
• and at least two air valves are provided at an input side on the primary mixing chamber;
• a primary passage into the primary combustion zone which is provided downstream of the primary mixing duct and fluidly connected to the primary combustion zone;
• wherein the primary mixing unit is arranged in such a way that it can mix the flue gas from the recirculation inlet with the primary air from the primary air duct by means of the at least two air valves, and
• wherein the primary mixing duct has a minimum length of 700 mm from beginning to end and is arranged adjacent to the heat exchanger, wherein the primary mixing duct is configured to preheat the mixture of flue gas and primary air upstream of the primary combustion zone, wherein the primary mixing chamber and the primary mixing duct are axially unaligned, and wherein the primary mixing chamber is configured to deflect a gas flow that enters the primary mixing chamber before the gas flow enters the primary mixing duct.