Furnaces – Refuse incinerator – Refuse suspended in or supported by a fluid medium
Patent
1989-11-29
1992-10-20
Yuen, Henry C.
Furnaces
Refuse incinerator
Refuse suspended in or supported by a fluid medium
122 4D, F23G 700
Patent
active
051560992
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an internal recycling type fluidized bed boiler in which combustion materials such as various coals, low grade coal, dressing sludge, oil cokes and the like are burnt by a so-called whirling-flow fluidized bed, the interior of a free board and a heat transfer portion provided downstream of the free board portion.
BACKGROUND OF THE INVENTION
Recently, utilization of coal as an energy source in place of petroleum has become more prevalent. In order to widely utilize coal which is inferior in its physical and chemical properties as a fuel to those of petroleum, development of processing and distribution of coal and of technology for promoting the utilization of coal has been in urgent demand. Research and development of a pulverized coal incinerating boiler and the fluidized bed boiler in the field of combustion technology have been positively advanced. With respect to combustion technology such as the above, utilization is restricted to certain kinds of coals in view of combustion efficiency, requirements of low NOx and low SOx. Also, problems such as the complexity of coal feeding systems and difficulty in controlling load fluctuations have become evident, which problems have been particularly evidenced in small and medium size boilers.
Fluidized bed boilers can be classified into two types as noted below according to the difference in a system wherein arrangement of heat transfer portions and combustion of unburnt particles flowing out from the fluidized bed are taken into account. conventional type fluidized bed boilers or bubbling type fluidized bed boilers)
In a non-recycling type, a heat transfer tube is arranged within a fluidized bed, and heat exchange is carried out by physical contact between the burning fuel and a fluidizing medium with high heat transfer efficiency. On the other hand, in a recycling type, fine unburnt materials, ash and/or a part of the fluidizing medium (recycling solid) are merged into a flow of combustion gas and guided to a heat exchanging portion arranged independently of the combustion chamber where combustion of the unburnt particles is continued and the circulating solid having undergone heat exchange is returned to the combustion chamber, the aforesaid title being given since the solid is recycled.
A non-recycling and a recycling type fluidized bed boiler will be described with reference to FIGS. 4 and 5.
FIG. 4 shows a non-recycling type fluidized bed boiler, in which air for fluidization fed under pressure from a blower (not shown) is injected from an air chamber 74 into a boiler 71 through a diffusion plate 72 to form a fluidized bed 73, and fuel, for example, granular coal, is supplied to the fluidized bed 73 for combustion. Heat transfer tubes 76 and 77 are provided in the fluidized bed 73 and an exhaust gas outlet of a free board portion, respectively, to recover thermal energy.
Exhaust gas cooled to a relatively low temperature is guided from an exhaust gas outlet of the free board portion to a convection heat transfer portion 78 to recover thermal energy and is discharged outside the system after contained particles are recovered at a cyclone 79. Ash recovered in the convection heat transfer portion is taken out through a tube 81 and discharged outside the system via a tube 82 together with ash taken out from a tube 80, a part thereof being returned to the fluidized bed 73 for reburning through the air chamber 74 or a fuel inlet 75.
FIG. 5 shows a recycling type fluidized bed boiler, in which air for fluidization fed under pressure from a blower (not shown) is blown from an air chamber 104 into a furnace 101 through a diffusion plate 102 to fluidize and burn granular coal containing lime as a desulfurizing agent to be supplied into the furnace as needed.
Unlike a non-recycling type fluidized bed boiler, injecting speed of fluidizing air blown through the diffusion plate 102 is higher than the terminal speed of the fluidizing particles, and therefore mixing of particles and gas is more actively effected and the
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Miyoshi Norihisa
Nagato Shuichi
Ohshita Takahiro
Ebara Corporation
Yuen Henry C.
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