Combined heat and power plant and a method for improving the burning process in a combined heat and power plant

A combined heat and power plant, comprising:

• a gasifier for converting a carbonaceous material into raw synthesis gas,
• a heat exchanger arranged to reduce the temperature of the raw synthesis gas formed in the gasifier by exchanging the heat of the raw synthesis gas into a heating medium to be used for heating and thereby forming cooled raw synthesis gas,
• a filtration unit for cleaning the cooled raw synthesis gas to form refined synthesis gas suitable as a fuel for an internal combustion engine,
• an internal combustion engine, wherein the refined synthesis gas is burnt to produce mechanical power,
• ducts for connecting different parts of the plant to each other, including a first raw gas duct led from the gasifier to the heat exchanger, a second raw gas duct led from heat exchanger to the filtration unit, a refined gas duct led from the filtration unit to the internal combustion engine and an exhaust gas duct to which the exhaust gas of the internal combustion engine is conducted,
• a raw gas burner arranged after the gasifier to burn the raw synthesis gas formed in the gasifier during the time when the refined synthesis gas is not utilized in the internal combustion engine, wherein
• the raw gas burner is arranged to heat the heating medium of the heat exchanger;
• and
• the refined gas duct is connected to the exhaust gas duct through a shut-off valve to prevent the refined synthesis gas from entering the exhaust gas duct during the use of internal combustion engine;
• the refined gas duct is connected to the internal combustion engine through a refined gas connection duct having a shut-off valve to prevent the cooled and filtered exhaust gas flowing through the refined gas duct to the exhaust gas duct from entering the internal combustion engine during the use of the raw gas burner;
• or
• the refined gas duct is connected to the exhaust gas duct and to the refined gas connection duct through one two-way directional valve which in its first position guides the exhaust gas coming from refined gas duct to the exhaust gas duct and in its second position guides the refined synthesis gas coming from refined gas duct in to the internal combustion engine through the refined gas connection duct.