Recuperative and conductive heat transfer system

Details Recuperative and conductive heat transfer system Recuperative and conductive heat transfer system

2000-12-18

2003-04-29

Bennett, Henry (Department: 3743)

Heat exchange

Intermediate fluent heat exchange material receiving and...

Solid fluent heat exchange material

C165S104110, C165S104150

Reexamination Certificate

active

06554061

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to heat transfer systems, and more specifically, to a recuperative and conductive heat transfer system that is operative to effect therewith the heating of a “working fluid” by means of the transfer of heat from hot regenerative solids to the “working fluid”. The term “working fluid” as employed herein is intended to refer to the “working fluid” of a thermodynamic cycle, e.g., steam or ammonia, as well as to a process feedstock. The source of heat by means of which the hot regenerative solids themselves become heated may take many forms with the most prevalent of those commonly being that of an internal heat source, e.g., being that of the hot gases, which are produced as the result of the combustion of fuel and air in some type of combustion chamber. However, this source of heat could also be in the form of an external heat source, e.g., be in the form of the hot gas exhaust from a turbine or other similar piece of equipment, or could be in the form of a hot process stream, which is produced as a consequence of some kind of chemical reaction.
With further reference to the matter of internal heat sources, furnaces for firing fossil fuels have long been employed as a device for generating controlled heat with the objective of doing useful work. To this end, the work application might he in the form of direct work, as with rotary kilns, or might be in the form of indirect work, as with steam generators for industrial or marine use or for the generation of electric power. A further differentiation, insofar as such furnaces is concerned, is whether the furnace enclosure is cooled, such as with waterwalls, or uncooled, such as with a refractory lining.
It is believed that such furnaces developed originally from a need to fire pottery, around 4000 B. C., and a need to smelt copper, in or about 3000 B. C. Hastening and improving combustion by the use of bellows to blow air into the furnace is believed to have occurred in about 2000 B. C.
Closely associated with such furnaces is the corresponding steam boiler. Such boilers appear to be of Greek and Roman origin and were employed for household services. The Pompeiian water boiler, incorporating the water-tube principle, is one of the earliest recorded instances, i.e., in approximately 130 B. C., of boilers doing mechanical work. To this end, the Pompeiian water boiler sent steam to Hero's engine, a hollow sphere mounted and revolving on trunnions, one of which permitted the passage of steam, which was exhausted through two right-angled nozzles that caused the sphere to rotate. This is considered by most people to have been the world's first reaction turbine.
For virtually the next 1600 years, furnaces in general and waterwall furnaces in particular were essentially a neglected technology. This can be partly ascribed to the fact that steam as a working.fluid had no application until the invention of the first commercially successful steam engine by Thomas Savery in 1698. In 1705, Newcomen's engine followed and by 1711, this engine was in general use for pumping water out of coal mines. Self-regulating steam valves are believed to have first come into existence in 1713.
Many varieties of firetube boilers were invented in the second half of the 18
th
century, culminating with the so-called Scotch marine boiler. As the name firetube boiler would imply, in the firetube boiler the tubes may be considered to be a component part of the furnace, with the combustion process-taking place within the tube bundles. However at the time, such units were limited, because of available steel-plate thicknesses, to operating pressures of about 150 psig. This was then followed by the development of the modem water-tube furnace for steam generation at higher pressures and in larger sizes than available with firetube boilers. Today, such modern water-tube furnaces for steam generation encompass all of the following: central-station steam generators, industrial boilers, fluidized-bed boilers, and marine boilers.
Of all of these various types of boilers, if it were necessary to classify the recuperative and conductive heat transfer system to which the present application is directed into one of these types of boilers, the recuperative and conductive heat transfer system to which the present application is directed, to the extent that an internal heat source is employed in connection with such a recuperative and conductive heat transfer system, would probably be considered to be more akin to a fluidized-bed boiler than to any of the aforementioned other various types of boilers. As such, the focus of the discussion hereinafter insofar as the prior art is concerned will thus be directed primarily to the fluidized-bed boiler type. To this end, fluidized-bed reactors have been used for decades in non-combustion reactions in which the thorough mixing and intimate contact of the reactants in a fluidized bed result in high product yield with improved economy of time and energy. Although other methods of burning solid fuels can generate energy with very high efficiency, fluidized-bed combustion can burn solid fuel efficiently at a temperature low enough to avoid many of the problems of combustion in other modes.
To those in the industry, it is well known that the word “fluidized” as employed in the term “fluidized-bed boiler” refers to the condition in which solid materials are given free-flowing fluid-like behavior. Namely, as a gas-is passed through a bed of solid particles, the flow of gas produces forces that tend to separate the particles from one another. At low gas flows, the particles remain in contact with other solids and tend to resist movement. This condition is commonly referred to as a fixed bed. On the other hand, as the gas flow is increased, a point is reached at which the forces on the particles are just sufficient to cause separation. The bed then becomes fluidized, that is, the gas cushion between the solids allows the particles to move freely, giving the bed a liquid-like characteristic.
The state of fluidization in a fluid-bed-boiler combustor depends mainly on the bed-particle diameter and fluidizing velocity. As such, there are essentially two basic fluid-bed combustion systems, each operating in a different state of fluidization. One of these two basic fluid-bed combustion systems is characterized by the fact that at relatively low velocities and with coarse bed-particle sizes, the fluid bed is dense, with a uniform solids concentration, and has a well-defined surface. This system is most commonly referred to by those in the industry as a bubbling fluid bed, because the air in excess of that required to fluidize the bed passes through the bed in the form of bubbles. The bubbling fluid bed is further characterized by modest bed solids mixing rates, and relatively low solids entrainment in the flue gas. While little recycle of the entrained material to the bed is needed to maintain bed inventory, substantial recycle rates may be used to enhance performance.
The other of these two basic fluid-bed combustion systems is characterized by the fact that at higher velocities and with finer bed-particle size, the fluid bed surface becomes diffuse as solids entrainment increases, such that there is no longer a defined bed surface. Moreover, recycle of entrained material to the bed at high rates is required in order to maintain bed inventory. The bulk density of the bed decreases with increasing height in the combustor. A fluidized-bed with these characteristics is most commonly referred to those by those in the industry as a circulating fluid bed because of the high rate of material circulating from the combustor to the particle recycle system and back to the combustor. The circulating fluid bed is further characterized by very high solids-mixing rates.
There are numerous examples to be found in the prior art of various forms of fluidized bed combustion systems, which have been devised over the course of time. Going back to as early as the late 1950's, an early example thereof, by wa

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