Circulating Fluidized Bed Combustor and a Method of Operating a Circulating Fluidized Bed Combustor

Abstract

A circulating fluidized bed combustor arrangement includes (a) a circulating fluidized bed reactor in which (i) a combustion chamber combusts a fuel material in a suspension of solid particles of a circulating fluidized bed, (ii) a first cyclone separator arrangement receives a mixture of gases and solid particles from the combustion chamber for separating a first fraction of the solid particles from the exhaust gases, and (iii) a solid particle return system connected to the first cyclone separator returns separated solid particles to the combustion chamber, (b) a heat transfer section including a water / steam heat exchanger section arranged after the first cyclone separator arrangement in the exhaust gas flow path, (c) a heat recovery device provided in connection with the combustion chamber, the first cyclone separator arrangement and the heat transfer section being arranged for recovering heat resulting from the combustion process in the combustion chamber, (d) a selective catalytic reduction system arranged in the exhaust gas flow path, after the heat transfer section, for removing NOx from the exhaust gas, (e) a device for injecting NOx reducing agent into the exhaust gases upstream of the selective catalytic reduction system, and (f) a second cyclone separator arrangement provided downstream of the first cyclone separator arrangement and upstream of the heat transfer section, in which a second fraction of the solid particles is separated form the exhaust gases.

Description

TECHNICAL FIELD AND BACKGROUND OF THE INVENTION[0001]The present invention relates to a circulating fluidized bed combustor and a method of operating a circulating fluidized bed combustor. Further, it relates to a novel method of controlling NOx.[0002]A circulating fluidized bed combustor arrangement of the prior art comprises a furnace, to which fuel, bed material and combustion air are introduced. When combusting the fuel, heat is generated, and both ash and exhaust gases are formed. The exhaust gases are taken to a separator, which separates solid particles, including the bed material, from the gases, and returns the solid particles back to the furnace. It is distinctive to the combustion process that the oxidation reaction of the fuel material is intended to be as complete as possible. Thus, the flue gases or exhaust gases do not contain substantially any unburned material.[0003]Structurally, the circulating fluidized bed (CFB) combustor generally includes a furnace having a bot...

AI Technical Summary

Benefits of technology

[0014]Another object of the present invention is to provide a circulating fluidized bed combustor that provides reduced amounts of pollutants to the atmosphere.

[0015]Yet another object of the present invention is to provide a method of operating a circulating fluidized bed combustor that provides reduced amounts of pollutants to the atmosphere.

[0018]Preferably, the second cyclone separator arrangement is provided immediately downstream of the first cyclone separator arrangement. In this way, the solid material may be separated from the exhaust gases at a high temperature, and the recycling of the particles back to the reactor is more feasible.

[0052]Several potential problems may be avoided with the present invention. The present invention provides a more reliable operation of the CFB combustor, e.g., because catalyst plugging due to a high dust load and alkalinity of ash may be eliminated or considerably reduced. With the present invention, it is also possible to minimize ash deposits which react with ambient moisture and develop hard deposits and acidity, thereby damaging the base material of the catalyst grid. Also, permanent plugging of the channels and pores may be avoided and / or the lifetime of the SCR catalysts is considerably increased.

Problems solved by technology

It is produced when nitrogen in the fuel combines with the excess oxygen in the combustion air, and is only a problem with fuel containing fuel bound nitrogen.

Thus, resulting in larger ash particles in the CFB systems.

As evidence from the above analysis, these two major problem areas remain in the direct use of SCRs in the CFB combustors: large ash particles and high dust loading.

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