A fluidized bed boiler plant and a method of preheating combustion gas in a fluidized bed boiler plant

Abstract

A fluidized bed boiler plant (10) and a method of preheating combustion gas fluidized bed boiler plant, the boiler plant comprising a furnace (12) and a combustion gas channel (24, 24b), and a water-steam cycle comprising an evaporator section (26), a superheater section comprising a last superheater (30') and a steam turbine (34), and a superheating path for conveying steam from the evaporator section (26) via the superheater section to the steam turbine, and a first combustion gas preheater (38, 38b), wherein the fluidized bed boiler plant comprises a second combustion gas preheater (40, 40b), a steam extraction line (46, 46b) attached in flow connection with the second combustion gas preheater and with the superheating path in a location upstream of the last superheater (30') for conveying steam from the superheating path to the second combustion gas preheater (40, 40b), wherein the method for preheating combustion gas comprises conveying steam from the superheating path from a location upstream of the last superheater via the steam extraction line (46, 46b) to the second combustion gas preheater (40, 40b), and transferring heat from the steam to the combustion gas in the secondcombustion gas preheater.

Description

technical field [0001] According to the preambles of the adjacent independent claims, the invention relates to a fluidized bed boiler plant and a method for preheating combustion gases in a fluidized bed boiler plant. More particularly, the present invention relates to a fluidized bed boiler plant and a method for preheating combustion gases in a fluidized bed boiler plant, which enable an advantageous operation of the boiler plant at particularly low loads. Background technique [0002] Today, fluidized bed boilers are often required to meet highly variable load requirements and thus to operate the boiler at very low loads. Conventional fluidized bed boilers typically have a minimum load of about 40% of full load, but today it would often be desirable to operate fluidized bed boilers at even lower loads (eg, 30-20%) of full load. Operating conventional fluidized bed boilers at very low loads is generally prevented by the requirement to maintain the bed temperature in the f...

AI Technical Summary

Problems solved by technology

However, this causes increased investment costs for the gas recirculation path and larger hot surfaces required due to the larger total exhaust flow, and increased auxiliary power consumption in the recirculation gas fan and the flue gas fan

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