Title of Invention

"LINEAR HORIZONTAL MULTI-MODULAR PEBBLE BED SYSTEM"

Abstract

This invention relates to a pebble bed system comprising a plurality of linearly configured horizontally oriented modular pebble sections or unit-beds (1) that function as the main heat transfer matrix, contained inside metallic cylindrical vessels, said modular unit-beds being provided with at least two dished end covers (2) that along with the cylindrical vessel form a closed pressure vessel chamber, said cylindrical vessel being provided with pipe nozzles (3,4,5,6) that act as the process gas flow interface between the pebble bed system and each of hot gas supply system, stack system, cold blow system and hot blow system, said flow nozzles being positioned on the top curved side of the cylindrical vessel, said nozzles being connected to process gas piping in different planes such that they do not interface with one another, said nozzles being connected to other systems through suitable valves (not shown), said unit-bed having a small spherical shaped objects called pebbles (7), said pebbles being made of ceramic material and thereby capable of withstanding very high temperatures of the order of 1000°C-2200°C, said pebbles surrounded all around by layers of fire-face refractory material (8), said refractory material either in the form of discreet bricks or castable ramming mass, covered with layers of amorphous insulating material (9) and fibrous insulation material (10), said unit-beds standing on their individual saddle support (11) and pedestal (12), said unit-beds (1) alongwith their refractory (8) and insulating material (9) lining serve to thermally withstand and insulate the hot environment and at the same time contain and support the mass of pebbles (7), said unit-beds when placed one behind the other in a horizontal and linear fashion give rise to a very large volume of heat transfer matrix suitable for heating large mass flow rates of high pressure gas streams to very high temperatures as would be typically required for a supersonic or hypersonic wind tunnel test facility, said large volume of linearly configured horizontal bed capable of storing extra-ordinary amounts of heat needed for effecting long duration flows and/or flows at near-constant outlet temperature.

Full Text

Subject matter of the Invention The present invention relates to a linear horizontal multi-modular pebble bed system. The invention particularly relates to a type of heat exchanger used for heat exchange among fluids. Classifiable under regenerative mixing type heat exchangers, commonly known as packed bed heaters or pebble bed heaters, these are widely used for heating air, water, steam, process fluids, chemical reagents, CO2 etc. One typical industrial application of packed bed regenerative heat exchanger is Cowper Stoves used in Iron and Steel industries. Another typical application of pebble bed is catalyst columns using ceramic spheres (pebbles) for promoting chemical reaction in the presence of a catalyst. Yet another emerging application of pebble bed systems is "Compact Nuclear Reactors". Application wise, pebble bed heaters have been preferred for preheating oxidizer to very high temperatures as required in MHD power plants and in the simulation of very high velocity air streams as needed in supersonic and hypersonic wind tunnel facilities. Prior Art Packed bed systems are being extensively used as chemical reactors, catalyst columns and reaction beds. Packed beds employing uniformly sized spherical elements are popularly referred to as "pebble bed" systems. Pebble bed heaters that are designed to handle gaseous media at high temperatures, far higher than the safe working limits of normal metallic tubes, pipes, plates, finned plates etc, use ceramic spherical pebbles as heat exchange medium. Pebble bed systems employing ceramic spheres are normally used as high temperature catalyst columns, high temperature heat exchangers and high-energy heat storage systems. Hence, these are called ceramic pebble bed heaters. Ceramic pebble bed heaters have been widely employed as hot air sources, where the temperature of the media to be heated is significantly high, often in the range of 1000-2000°K. Pebble bed heaters are also employed for supplying high-pressure air streams in large quantities (mass flow rates) required for expansion and realization of high velocity flows in supersonic and hypersonic wind tunnel facilities. In order to avoid excessive cooling that accompanies such expansion through large pressure differentials, the high-pressure steam of air is often pre-heated to high temperatures in pebble bed systems. Very often the kind of flow rates required achieving a reasonable high velocity, would necessitate usage of multiple pebble bed systems to operate in tandem. Search was carried out for different combinations such as pebble, bed and heaters. Salient search results are reproduced hereinbelow. As can be seen most of the patents from the aforementioned searches relate to pebble bed reactors. Three among the list refer to pebble bed heaters employed for heating a process fluid and are their salient aspects are described briefly here below. US Patent # 5,542,022 - describes a compact portable apparatus and method for heating gases for periods ranging from about one tenths of a second to several minutes to temperatures as high as 2700°C. Based on electrical heating, this patent describes a short duration pulsed flow system that is reliable, portable and suitable for Magneto Hydro Dynamic and wind tunnel applications. The above patent describes an electrically heated system that is capable of producing high temperature pulsed flows required for typical applications like MHD etc. It is different from the proposed invention, which is essentially based on a heating gas driven, as would be a normal fossil fuel fired heater. US Patent # 5,299, 866 and 5,197,323 describe a vertically oriented pebble bed evaporator with baffles for producing an high temperature high pressure vapour blast for a shock tube assembly. The above patents describe a single vessel heater system that typically addresses evaporation of fluids and generation of squirts of pulsed vapours flows. The very orientation aspect and its merits/de-merits thereof makes each of these patents distinctly different from the proposed invention, which derives its characteristics advantages from a linear and horizontal orientation. Rest of the patent search results predominantly cover either pebble bed based nuclear reactors or chemical reaction columns or some other designs addressing pebble bed based driers, solar heaters and specialty heaters etc. Limitation / disadvantages of the prior art Conventional pebble bed heaters are usually configured as vertical cylindrical vessels, in which air enters the hot pebble bed from bottom and travels upwards as it gets heated. When a higher quantity of air is to be handled, the vessel diameter and height proportionately increases. However, the size of the individual cylindrical vessel cannot increase unconditionally owing to manufacturing/fabrication limitations and transportation ease. Beyond a particular extent tandem operating multiple vessels are usually employed. Multiple vessels require inter vessel connections and duct/pipe systems that serve to branch the flows and consolidate flows from various individual heaters. The invention described herein relates to systems of pebble bed heat exchangers specifically configured for storing and supplying extremely large quantities of thermal energy for effecting very large enthalpy blow downs involving large mass flows of high pressure, high temperature air. The invention specifically describes unique design configurations and layout of modular pebble bed heater systems that can typically deliver very large quantities high-pressure high-temperature air supply, commonly referred to as 'blow downs'. The present invention obviates multiplicity of conventional heater configurations for achieving a large mass flow rate supply, thereby offering an engineering solution that is compact, is more economical to build and operate, has lesser foot-print and is least bothersome for operation and maintenance in addition to being very efficient amongst comparable options.STATEMENT OF INVENTION According to this invention there is provided a pebble bed system comprising a plurality of linearly configured horizontally oriented modular pebble sections or unit-beds that function as the main heat transfer matrix, contained inside metallic cylindrical vessels, said modular unit-beds being provided with at least two dished end covers that along with the cylindrical vessel form a closed pressure vessel chamber, said cylindrical vessel being provided with pipe nozzles that act as the process gas flow interface between the pebble bed system and each of hot gas supply system, stack system, cold blow system and hot blow system, said flow nozzles being positioned on the top curved side of the cylindrical vessel, said nozzles being connected to process gas piping in different planes such that they do not interface with one another, said nozzles being connected to other systems through suitable valves (not shown), said unit-bed having a small spherical shaped objects called pebbles, said pebbles being made of ceramic material and thereby capable of withstanding very high temperatures of the order of 1000°C-2200°C, said pebbles surrounded all around by layers of fire-face refractory material, said refractory material either in the form of discreet bricks or castable ramming mass, covered with layers of amorphous insulating material and fibrous insulation material, said unit-beds standing on their individual saddle support and pedestal, said unit-beds alongwith their refractory and insulating material lining serve to thermally withstand and insulate the hot environment and at the same time contain and support the mass of pebbles, said unit-beds when placed one behind the other in a horizontal and linear fashion give rise to a very large volume of heat transfer matrix suitable for heating large mass flow rates of high pressure gas streams to very high temperatures as would be typically required for a supersonic or hypersonic wind tunnel test facility, said large volume of linearly configured horizontal bed capable of storing extra-ordinary amounts of heat needed for effecting long duration flows and/or flows at near-constant outlet temperature. Linear horizontal multi-modular pebble bed systems offer a solution that is technologically viable, easier to design and install and economical to operate and own for supplying large quantities of high-pressure, high-temperature streams of air/gas, as would be required by high-enthalpy facilities like supersonic and hypersonic wind tunnel facilities. Foremost of the objectives of the linear horizontal multi-modular pebble bed systems is to offer a techno-economically viable option for pebble bed heater systems capable of supplying very large flow rates of high pressure, high temperature flow. Another object of the invention is being a technologically viable system of pebble bed heaters that can handle, heat and supply very large flow rates of high-pressure, high temperature air or any other gaseous media as would be typically required in, but not restricted to, supersonic and hypersonic wind tunnel facilities. In addition to being a novel engineering option this is also an economically competitive alternative. Further, it also serves to store extraordinarily large quantities of thermal energy for catering to high enthalpy blow-down test facilities that need substantially long periods of "blow-down' at near constant parameters. Still another objective of the invention is to offer a system that is easy to design, install and operate. Linear horizontal multi-modular pebble bed systems comprise of horizontally configured linear modules of pebble bed systems (PBHs), contrary to the vertically standing conventional PBHs. Because of this feature, higher heat exchange bed volume does not translate into taller structures. Attendant problems of higher structural cost, stronger foundation, designing for seismic and wind load integrity etc are also obviated. Yet another object of this invention is to improve capability to function under varying operating conditions. Conventionally pebble bed system is designed for the most severe operating condition and at part load operations the system may not function most optimally. Contrarily multi-modular configuration makes part load or off-design operation also as efficient by selectively including or isolating certain modules and employing only an optimal number of modules that promise efficient operation. If suitable configured in particular layouts so as to form banks of networked systems, widely different regimes of operation can be easily catered to with minimal operational complexity. A still further objective of this invention is to offer a solution that does not call for very sophisticated fabrication techniques and manufacturing facilities. Conventionally designed single vessel pebble bed systems as well as multi-vessel systems would have to employ as large a diameter as possible for shell and as thick a vessel as possible to operate under high pressure but one that employs a basic technology that is considered 'normal'. Modular configuration and "multiples" of such modules being the central idea of this invention, it purports to effectively eliminate / alleviate most of the problems associated with large diameter, thick-walled, multi-vessel design and tandem operation. Individual modules are horizontally oriented cylindrical heater sections, having optimal diameter, shell thickness and shell length, which could be reasonably built with normal fabrication methods. Larger bed volumes simply cause two or more 'modules' to be pieced together; usually welded on the circumference of the shell. Another distinctive advantage of the invention is to reduce or limit the severity of the operating conditions of the pebble bed system parts when the size of the unit increases. Owing to its inherent layout, this method results in fewer end covers (dished ends). Further, since the shells are horizontally oriented, the cylindrical walls themselves act as bed support, obviating the need to have a separate load-carrying bed support. This is a major advantage especially when large sized units are involved. Further, when configured in particular user-defined arrangements, this invention lends itself very comfortably to form banks of networked systems for variable operating conditions. The pressure drop suffered by the flow is also far less than comparable systems. Thus, the horizontal multiple modular pebble-bed heater forms an economic and ideal engineering choice for heating large mass flow rates of high-pressure air/gas to high temperature ranges. Fig. 1 gives the salient component list of a typical pebble-bed heater system. Figs. 1A and IB show both single vessel and multi-vessel conventional pebble-bed heating systems. Each of the individual vessels in this arrangement is to be separately constructed, replete with its own main shells (1), dished-end covers (2), nozzle pipes (3,4,5,6), pebbles (7), shell flanges (13), bed supports (14) and structural supports (10, 11). Multiple vessels are connected using interconnecting duct systems (15). When high enthalpy pebble bed heat storage systems are designed for high pressures, it necessitates employing thick-walled vessels. While designing for heating large quantities of flow (higher mass flow rates) such flow of fluids through the bed causes velocity to increase. However, in order to prevent bed fluidization, bed velocities have to be kept limited to threshold values. This causes the bed diameter to be made larger. This causes the shell thickness to go up further. High operating temperatures and a longer duration blow cycle (as is typically needed for high enthalpy flow simulation facilities) further compound this. For a given operating pressure and mass flow rate, it requires a larger volume of bed; this means for any given bed diameter a taller pebble bed is needed to achieve higher temperatures at outlet and minimal temperature drop during the chosen blow cycle. Taller structures mean higher initial cost and stringent foundation requirements. Further, higher operating temperature necessitates internal thermal insulation to be employed. This would result in a stouter and stronger vessel. While internal refractory lining and insulation cause to increase the vessel diameter, un-insulated design would result in much thicker shell walls for a given operating pressure owing to lesser allowable stresses at higher operating temperatures. Thus, pebble bed heaters for high enthalpy blow down facilities like a typical hypersonic wind tunnel facility etc with an operating condition of high pressure, high temperature and high mass flow rates cumulatively result in a very formidable and challenging vessel design that needs a very large diameter pebble bed heater that is also very tall and made of very thick shell wall. Economics of design, manufacturing feasibility, compliance to standard design codes and availability of technology etc., collectively pose independent limits on the dimensions of a single vessel that can be fabricated using known and available resources. For example, a shell diameter of 3000 mm to be fabricated out of a 200 mm thick plate represent a reasonable upper limit from unencumbered fabrication point of view. If the design of the pebble-bed heater vessel is to be larger than this, necessarily the vessel has to be split into two or more vessel to be operated in tandem. Thus, high pressure, high temperature and high flow vessels have to be invariably designed as a system comprising of multiple vessels, configured with connecting system of ducts, valves and fittings. Designs involving multiple vessels suffer from shortcomings arising out of higher raw material content, higher thermal lining and insulation material consumption (vessel shells and end covers) for the same thermal duty, multiple end closure 'dished ends', higher fabrication and inspection costs, higher capital investment owing to the larger space requirement, multiple civil foundation requirements, multiple valves and fittings, multiple instrumentation and controls etc. They could also suffer from possible mismatch in operating conditions between the different parallel-operating pebble-bed systems leading to difficulty in process control. Typical hot air facilities needed to simulate supersonic and hypersonic flows with reasonably large wind tunnel proportions may often require huge mass flow rates and hence would require a battery of conventionally designed pebble bed heater to be employed in tandem. Description With reference to the drawings a typical linear horizontal multi-modular pebble bed system would employ 'unit-bed' sections (1) that are cylindrical sections of pressure vessels, which can be designed and fabricated with relative ease using conventional and straightforward manufacturing techniques. Multiple 'unit-beds' (1) configured together will form a continuous cylindrical heat exchange matrix, contained in a conventionally fabricated metallic pressure vessel. The unit-bed vessels are bodily bound at extreme ends by formed metallic dished ends (2), that could be either hemispherical or ellipsoidal in shape. Located on the top surface of the 'unit-beds' are nozzle interface provisions that connect the PBH to other systems both upstream and downstream. During the heating process cycle, hot gas from combustor enters the PBH through 'hot gas entry nozzle (3) and after transferring the heat content to pebbles (7) contained in the unit-bed (1) the flue-gas leaves the PBH through stack nozzle (4). Likewise during the blowing process cycle, air at ambient conditions enters the PBH through cold blow entry nozzle (5) and upon picking up heat from the pebbles (7) leaves the PBH as hot air through 'hot blow nozzle' (6). The nozzles connect to process piping or interfaces to other systems in such a way that they do not cross each other and no two pipes of adjacent systems are coplanar. The unit-beds (1) are externally welded at the pressure boundary and internally continuous at the pebble space. The pebbles (7) are the heat transfer matrix that alternatively serves to absorb the heat from hot gases that pass through them and store the absorbed heat as their internal energy. The pebbles therefore increase in their temperature during heating cycle. Likewise during the blow cycle, the fluid to be heated enters through 'cold blow entry nozzle' (5) and picks up the stored heat from pebbles (7) and leaves as 'hot fluid' or 'hot blow' through 'hot blow nozzle' (6). The unit bed (1) is internally insulated with multiple layers containing of refractory fire-face (8), amorphous insulation (9) and fibrous insulation material (10). The unit beds are supported adequately at cylindrical saddle (11) and sliding base (12). Multiples of such unit-beds would have equi-spaced sets of the above described body parts repeated at specified spatial interval. The toral flow would enter the system through plurality of inlets (3,5) and similarly outflows are through plurality of outlets (4,6). The flow entering through the inlets, passes through different 'unit-bed' of the pebble bed system and finally exits through the outlets after getting heated to the required extent. Most significantly, the linear horizontal configuration obviates the need to have separate pebble bed support (14) as opposed to a conventional configuration. The cylindrical thermal lined surface itself acts as bed support and thereby promotes compactness of the system. Further, only one pair of dished end is required for the entire system, as opposed to 'one pair of dished ends to every vessel' of the conventional style. This marks a significant simplification and can reduce the overall cost considerably. Significantly, the horizontally oriented bed causes the temperature to be so distributed that no excessive radiation loss from hot surface to dome is encountered, contrasted to the ease of radiation from the top surface of the vertically oriented bed. This also makes heating the entire bed to same temperature possible, which in the vertical style could be limited by the material of construction, especially at higher temperatures. Various benefits achievable using linear horizontal multi-modular pebble bed system can be summarized as under. Factors that lead to improve economy and capital savings include savings in manufacturing and integrating end closing dished heads. For conventional multiple separate vessels, each vessel would require two dished ends that have to be separately press-formed and welded on the shell. Whereas, the said invention's configuration needs only minimum numbers of end covers, just two for each linear train. As shown in Fig.3, most of the configurations would require just two dished ends. Apart from the metal content of the dished end enclosure, enormous savings in refractory lining and insulation lining are possible, as the bed units are integral. Additionally, the functional component that supports the dead weight of the individual bed in vertical vessels is eliminated, since in horizontally oriented beds are inherently self-supporting nature, leading to design ease in addition to improved economy. Civil foundation and load related costs are less severe, improving capital savings. Features that lead to improve operating economy include the proposed configuration resulting in optimal pressure drop, as the total flow is shared between multiple fluid entry / exists passages and unit-bed. The bed velocities are relatively lesser, and larger flow area is available from the multiple modules. Further, compared to the vertical conventional configuration, linear horizontal units have much less exposed area that radiate / convect out heat. Thus, reduced exposed surface area leads to lesser heat loss to external atmosphere, improving operating performance. Features that lead to improved ease of system design, erection and operation include, the system's capability to be easily scaled up (extended to any higher capacity), by merely adding further "modules of unit-bed". The basic idea yields itself to be extended to configure "PBH-farms", an arrangement employing a multitude of vessels arranged in fashions that permit selective part load operations as well as full load operation as per requirement The arrangement can be suitably altered to suit the conveniences of system piping arrangement, as shown hi Fig.4. WE CLAIM; 1. A pebble bed system comprising a plurality of linearly configured horizontally oriented modular pebble sections or unit-beds (1) that function as the main heat transfer matrix, contained inside metallic cylindrical vessels, said modular unit-beds being provided with at least two dished end covers (2) that along with the cylindrical vessel form a closed pressure vessel chamber, said cylindrical vessel being provided with pipe nozzles (3,4,5,6) that act as the process gas flow interface between the pebble bed system and each of hot gas supply system, stack system, cold blow system and hot blow system, said flow nozzles being positioned on the top curved side of the cylindrical vessel, said nozzles being connected to process gas piping in different planes such that they do not interface with one another, said nozzles being connected to other systems through suitable valves (not shown), said unit-bed having a small spherical shaped objects called pebbles (7), said pebbles being made of ceramic material and thereby capable of withstanding very high temperatures of the order of 1000°C-2200°C, said pebbles surrounded all around by layers of fire-face refractory material (8), said refractory material either in the form of discreet bricks or castable ramming mass, covered with layers of amorphous insulating material (9) and fibrous insulation material (10), said unit-beds standing on their individual saddle support (11) and pedestal (12), said unit-beds (1) alongwith their refractory (8) and insulating material (9) lining serve to thermally withstand and insulate the hot environment and at the same time contain and support the mass of pebbles (7), said unit-beds when placed one behind the other in a horizontal and linear fashion give rise to a very large volume of heat transfer matrix suitable for heating large mass flow rates of high pressure gas streams to very high temperatures as would be typically required for a supersonic or hypersonic wind tunnel test facility, said large volume of linearly configured horizontal bed capable of storing extra-ordinary amounts of heat needed for effecting long duration flows and/or flows at near-constant outlet temperature. 2. A pebble bed system as claimed in claim 1 wherein its linear and horizontal orientation support the mass of pebbles on its cylindrical surface itself thus obviating the need to have separate bed support (14) or 'grid/grade'. 3. A pebble bed system as claimed in claim 1 wherein its enormous heat storage capacity is capable of supplying hot flow medium at any select temperature within the design range, for very large lengths of time, say upto 1 hour, without any appreciable drop in final temperature. 4. A pebble bed system as claimed in claim 1 and 2 wherein outer pressure vessel has most simples geometric forms like cylindrical sections and fewer number of dished ends and the whole being system is manufactured with most common manufacturing processes and conventional methods like welding etc. 5. A pebble bed system as claimed in Claim 1 to Claim 3 wherein its modular configuration performance over a wide range of operating parameters, especially at very low part loads. 6. A pebble bed system as claimed in Claim 1 to Claim 3 involve very large enthalpy such as high pressure and temperature of flow, like typically encountered in supersonic and hypersonic wind-tunnel facilities. 7. A pebble bed system as herein described and suitable for storage of very large quantities of heat as thermal inertia or internal energy of the heat exchange matrix controlled release of such stored heat through gaseous medium that flow past the said pebble bed.

Documents:

600-DEL-2004-Abstract-(07-01-2010).pdf

600-DEL-2004-Claims-(07-01-2010).pdf

600-del-2004-claims.pdf

600-DEL-2004-Correspondence-Others-(07-01-2010).pdf

600-del-2004-correspondence.pdf

600-del-2004-correspondene-others.pdf

600-del-2004-correspondene-po.pdf

600-DEL-2004-Description (Complete)-(07-01-2010).pdf

600-del-2004-description (complete).pdf

600-del-2004-description (provisional).pdf

600-del-2004-description.pdf

600-del-2004-drawings (provisional).pdf

600-DEL-2004-Drawings-(07-01-2010).pdf

600-del-2004-drawings.pdf

600-del-2004-form-1.pdf

600-del-2004-form-18.pdf

600-del-2004-form-2.pdf

600-del-2004-form-3.pdf

600-del-2004-form-5.pdf

600-del-2004-form1.pdf

600-del-2004-form2 (provisional).pdf

600-del-2004-form2.pdf

600-del-2004-form26.pdf

600-del-2004-form3.pdf

600-del-2004-form5.pdf

600-DEL-2004-GPA-(07-01-2010).pdf

600-del-2004-gpa.pdf