US20110100583A1 - Reinforced thermal energy storage pressure vessel for an adiabatic compressed air energy storage system - Google Patents

Abstract

A thermal energy storage system comprises a pressure vessel configured to withstand a first pressure, wherein the pressure vessel has a wall comprising an outer surface and an inner surface surrounding an interior volume of the pressure vessel. The interior volume of the pressure vessel has a first end in fluid communication with one or more compressors and one or more turbines, and a second end in fluid communication with at least one compressed air storage component. A thermal storage medium is positioned in the interior volume, and at least one reinforcement structure is affixed to the outer surface of the wall, wherein the at least one reinforcement structure configured to reinforce the wall to withstand a second pressure greater than the first pressure.

Description

BACKGROUND OF THE INVENTION
• Embodiments of the invention relate generally to compressed air energy storage (CAES) systems and, more particularly, to thermal energy storage (TES) pressure vessels in an adiabatic CAES system.
• CAES systems allow the generation of electricity without producing substantial emissions and/or consuming vast quantities of natural resources. CAES systems typically include a compression train having one or more compressors. The one or more compressors compress intake air in a compression stage for storage in a cavern, porous rock formation, depleted natural gas/oil field, or other compressed air storage component. The compressed air is then later used to drive turbines to produce electrical energy in an energy generation stage, which can in turn be provided to the utility grid. Often, if utility energy is used to power the compression train during the compression stage, the compression train operates during the off-peak hours of utility plants. The energy generation stage of the CAES in turn typically operates during high energy demand times. Alternatively, energy from renewable sources, such as energy from wind mills or solar panel arrays, may be used to power the compression train during the compression stage to compress and deliver air to the compressed air storage location (e.g., a cavern). In this way, the compression train may be operated during times other than off-peak hours, and existing utility energy may be preserved.
• One type of CAES system is known as a diabatic-CAES system. In a diabatic-CAES system, heat generated by the compression train is typically lost to the ambient environment. That is, the heat of compression may be largely present when entering the cavern or other compressed air storage component, but its energetic value and availability is diminished as the compressed air mixes with the cavern air and further cools to ambient temperature during storage. Thus, when the compressed air stored in the cavern or compressed air storage component is to be used to drive one or more turbines to produce electrical energy, the compressed air is typically reheated prior to entering the turbines. This reheating step is typically performed using a natural gas-fired recuperator positioned between the compressed air storage component and the one or more turbines. Due to this reheating step, the overall efficiency of the diabatic-CAES system is reduced, and the use of natural gas to fuel the recuperator leads to carbon emissions and natural resource consumption.
• Adiabatic-CAES, or ACAES, systems are capable of improving system efficiency by capturing and storing the heat of compression for later use. In such a system, one or more thermal energy storage (TES) units are positioned between the compressor and the cavern. Typically, a TES unit contains therein a medium for heat storage, such as concrete, stone, a fluid (e.g., oil), a molten salt, or a phase-change material. Hot air from the compression stage is passed through the TES unit, thereby transferring its heat of compression to the medium in the process. Thus, unlike diabatic-CAES systems, ACAES systems do not lose all of the heat generated by the compression train, but instead store some of the heat within the TES unit or units. The compressed air then enters the cavern at or near ambient temperature.
• When the compressed air stored within the cavern or other compressed air storage unit is to be withdrawn to drive the one or more turbines to produce electrical energy, the compressed air passes back through the TES unit, thereby reheating the compressed air prior to entry into the turbine or turbines. In this way, ACAES systems do not necessitate additional natural gas-fired recuperation to reheat the compressed air exiting the cavern or other compressed air storage component. Thus, ACAES systems provide improved efficiency over diabatic-CAES systems, with fewer (if any) carbon emissions and little to no natural resource consumption.
• TES units built to effectively store heat generated during the compression cycle of the compression train are constructed to withstand the high heat fluctuations and high pressure associated with ACAES systems. For example, the compressed air temperature exiting the compression train may vary from 250° C. to 750° C., while the temperature of the compressed air entering the TES unit from the cavern is at or near ambient temperature. Likewise, the TES units are designed to withstand pressures of 65-85 bar. To withstand such high temperatures and pressures, current proposals for TES units involve the construction of large concrete cylinders filled with a medium for heat storage. Due to their large diameter, these TES units are formed having thick, pre-stressed and steel-reinforced concrete walls, which enable the TES unit to withstand the high tension forces in the wall created by the pressure therein. However, construction of such thick concrete walls leads to substantial engineering difficulties and high costs, thereby reducing the feasibility of implementing an ACAES system as opposed to a less efficient diabatic-CAES system. Furthermore, high operating temperatures and temperature cycles induce damaging thermal stresses into the concrete walls, and these stresses are amplified as the concrete walls grow thicker.
• Therefore, it would be desirable to design an apparatus and method that overcomes the aforementioned drawbacks related to TES unit construction.
BRIEF DESCRIPTION OF THE INVENTION
• Aspects of the invention provide a system and method for a TES unit having at least one reinforced structure affixed thereto to allow the TES unit to withstand both high pressures and high temperatures. The at least one reinforced structure enables the wall of the TES unit to have a minimal thickness.
• In accordance with one aspect of the invention, a thermal energy storage system is disclosed, the thermal energy storage system comprising a pressure vessel configured to withstand a first pressure, wherein the pressure vessel has a wall comprising an outer surface and an inner surface surrounding an interior volume of the pressure vessel. The interior volume of the pressure vessel has a first end in fluid communication with one or more compressors and one or more turbines, and a second end in fluid communication with at least one compressed air storage component. A thermal storage medium is positioned in the interior volume, and at least one reinforcement structure is affixed to the outer surface of the wall, wherein the at least one reinforcement structure configured to reinforce the wall to withstand a second pressure greater than the first pressure.
• In accordance with another aspect of the invention, a method of forming a thermal energy storage pressure vessel is described. The method comprises forming a wall having a predetermined height and thickness, wherein an inner surface of the wall bounds an interior volume therein. The method further comprises affixing a reinforcement structure to a surface of the wall at a first location, affixing at least one additional reinforcement structure to a surface of the wall at another location along the height of the wall, and disposing a porous thermal storage medium within the interior volume.
• In accordance with yet another aspect of the invention, a thermal energy storage pressure vessel is disclosed, the thermal energy storage pressure vessel comprising a concrete cylindrical wall bounding an interior volume, wherein the interior volume is configured to allow air passage therethrough, and at least one reinforcing structure affixed to an outer surface of the concrete cylindrical wall. The thermal energy storage pressure vessel further comprises a porous thermal matrix material disposed within the interior volume of the concrete cylindrical wall, wherein the porous thermal matrix material is configured to allow air passage therethrough.
• Various other features and advantages will be made apparent from the following detailed description and the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
• The drawings illustrate preferred embodiments presently contemplated for carrying out the invention.
• In the drawings:
• FIG. 1 is a schematic arrangement of an ACAES system according to an embodiment of the present invention.
• FIG. 2 is a side view of a TES unit in accordance with an embodiment of the present invention.
• FIG. 3 is a cross-sectional view of the TES unit ofFIG. 2 in accordance with an embodiment of the present invention.
• FIG. 4 is a side view of a TES unit in accordance with an another embodiment of the present invention.
• FIG. 5 is a cross-sectional view of the TES unit ofFIG. 4 in accordance with another embodiment of the present invention.
• FIG. 6 is a cross-sectional view of a TES unit in accordance with yet another embodiment of the present invention.
DETAILED DESCRIPTION
• According to embodiments of the invention, a system is provided that comprises a TES unit having at least one reinforced structure affixed thereto to allow the TES unit to withstand high pressure and temperature fluctuations.
• First, referring toFIG. 1, a schematic arrangement of the primary elements of a conventional ACAES system is shown. ACAESsystem100 comprises anelectric motor102 coupled to a low-pressure compressor104.Electric motor102 may be electrically powered via conventional means, i.e., the utility grid, during off-peak utility hours. Alternatively,electric motor102 may be powered by electricity provided via wind farms, solar arrays, or other renewable sources.Electric motor102 powers low-pressure compressor104 such that low-pressure compressor104 pressurizesintake air106. Pressurizedair108 from low-pressure compressor104 is then provided to a high-pressure compressor112 to enable the air to undergo further compression. Similar to low-pressure compressor104, high-pressure compressor112 is powered by anelectric motor110.Electric motor110 may also be powered by the utility grid or by renewable sources such as wind farms and solar arrays. While ACAESsystem100 shows the use of two compressors in a “compression train”, it is to be understood that more or fewer compressors could be used.
• As the air passes through respective low-pressure compressor104 and high-pressure compressor112, the air is pressurized to a level of 65-85 bar and subsequently heated to a temperature of up to 650° C. This pressurized,heated air114 then enters a thermal energy storage (TES)unit116.TES unit116 typically includes a porous thermal storage medium disposed therein, the porous thermal storage medium capable of retaining a substantial amount of the heat emitted byair114 as it passes throughTES unit116. The porous thermal storage medium may be a variety of solid materials, such as natural stone, ceramics, concrete, cast iron, or a combination of ceramics and salt. Alternatively, the porous thermal storage medium may be a liquid material, such as a combination of nitrate salt and mineral oil.
• Afterheated air114 passes throughTES unit116,compressed air118 exitsTES unit116 at a lowered temperature to enablecompressed air118 to be stored in acavern122 or other compressed air storage component. Prior to enteringcavern122, though,compressed air118 may need to be further cooled by anoptional intercooler120 such thatcompressed air118 enterscavern122 at a maximum temperature of approximately 50° C., for example.Cavern122 enables air pressurized to a level of about 60-80 bar to be stored for an extended period of time without significant compression losses.
• Referring still toFIG. 1,compressed air124 may be discharged fromcavern122 when use of the stored air is desired for the generation of electricity.Compressed air124 exitscavern122 andre-enters TES unit116 at a temperature of approximately 20-50° C. As the compressed air passes through the porous thermal storage medium ofTES unit116, it is reheated to a temperature of up to 600° C., a temperature near that ofheated air114 previously discharged from high-pressure compressor112. This reheatedcompressed air126, which at this stage is pressurized to a level of about 55-75 bars, then enters asteam turbine128, which is powered by reheatedcompressed air126. Unlike diabatic-CAES systems,compressed air126 has been reheated withinTES unit116, and thus there is no need for additional heat recuperation or gas firing at the steam turbine to reheat the compressed air. Assteam turbine128 operates,exhaust air130 is discharged therefrom, andsteam turbine128 powers anelectrical generator132. Electrical energy generated bygenerator132 may then be provided to the utility grid for consumption. As can readily appreciated,ACAES system100 represents a method of generating electricity that can greatly reduce, if not eliminate, natural resource consumption and/or carbon emissions in the production of electrical energy.
• As discussed above with respect toFIG. 1,TES unit116 may be subjected to significant pressures (65-85 bar) and temperatures (up to 650° C.) during operation ofACAES system100. As a result,TES unit116 is constructed to withstand such high pressure and temperature levels. Referring toFIGS. 2 and 3,TES unit116 according to an embodiment of the invention is shown.FIG. 2 illustrates a side view ofTES unit116.TES unit116 is illustrated as a cylindrical pressure vessel having awall202 of a predetermined length and thickness.TES unit116, however, is not limited to cylindrical shapes, and may be of any suitable shape.Wall202 is generally formed of concrete, but may be constructed using any material of suitable strength and rigidity, such as steel.Cross section204 ofTES unit116 further shows that a plurality ofreinforcement structures206 are affixed to anouter surface218 ofwall202 along a length ofTES unit116. While a plurality ofreinforcement structures206 is shown, it is to be understood that embodiments of the invention are not limited to the number and placement of thereinforcement structures206 shown.
• FIG. 2 further shows a cut-away cross section208 ofTES unit116. As can be seen by cut-away cross section208, eachreinforcement structure206 comprises at least onerod210 passing entirely through aninterior volume212 andwall202.Interior volume212 contains therein a porous thermal storage medium, such as natural stone or a ceramic material, which is designed to absorb and retain heat from the compressed air passing throughTES unit116, as described above. Eachrod210 is affixed to an outer surface ofwall202, thereby providing structural reinforcement withinTES unit116.
• Referring now toFIG. 3, a cross-sectional view ofTES unit116 according to an embodiment of the invention is shown. As can be seen inFIG. 3, a plurality ofrods210 are configured to pass through bothwall202 andinterior volume212, forming a spoke-shaped framework withininterior volume212.Rods210 are preferably made of steel, but may be made of any suitable material capable of withstanding high pressures and temperatures.Rods210 are fixedly attached to theouter surface218 ofwall202 byanchors214.Anchors214 may be affixed to theouter surface218 ofwall202 by any appropriate means, e.g., through bolting or welding.Rods210 are also coupled at acommon centerpoint hub216 located withininterior volume212. Preferably,rods210 are of a sufficient length to pass entirely throughwall202 on opposite sides thereof and throughinterior volume212 andcenterpoint hub216 to be affixed to two opposinganchors214. For example, as shown inFIG. 3, areinforcement structure206 has fourrods210 interconnected bycenterpoint hub216. Eachrod210 is attached toouter surface218 ofwall202 via a pair ofrespective anchors214 attached to opposite sides ofwall202.
• According to another embodiment, rather than extending entirely throughwall202 andinterior volume212 as a single rod,rods210 may be configured to pass throughwall202 and extend towardcenterpoint hub216. In this manner, one end of eachrod210 is retained by arespective anchor214, while the other end is retained by or coupled tocenterpoint hub216.
• It is to be understood that the configuration shown inFIG. 3 is merely exemplary and that while four or eightrods210 are shown as described above, embodiments of the invention include using more orfewer rods210 and anchors214 in eachreinforcement structure206.
• By reinforcingTES unit116 in the fashion shown byFIGS. 2 and 3, wall stresses caused by high air pressure withinwall202 can be substantially relieved. As a result,wall202 can be constructed with a reduced overall thickness, asreinforcement structures206 act to relieve stress onwall202 that was previously addressed through increased wall thickness. With such reduced wall thickness,TES unit116 will also not be subject to the substantial thermal stresses present in pressure vessels having thick walls. Furthermore,TES unit116 is easier and less expensive to both construct and transport over conventional TES units. As such, embodiments of the invention allow for construction and adoption of ACAES systems as viable alternatives for producing electrical energy.
• Referring now toFIGS. 4 and 5, another embodiment of the present invention is shown.FIG. 4 illustrates a side view of aTES unit416 comprising awall402 having a predetermined length and thickness. WhileTES unit416 is shown to be cylindrical, it is not limited as such, and may be of any suitable shape.Wall402 is generally formed of concrete, but may be constructed using any material of suitable strength and rigidity, such as steel.Cross section404 ofTES unit416 shows a plurality ofreinforcement structures406 affixed about an outer surface ofwall402 along a length ofTES unit416. WhileFIG. 4 shows a plurality ofreinforcement structures406 affixed alongTES unit416, the number and placement ofreinforcement structures406 is not limited to that shown, as it is possible one ormore reinforcement structures406 affixed to wall402 according to embodiments of the present invention.
• FIG. 4 further shows a cut-away cross section408 ofTES unit416. Unlikereinforcement structures206 described above with respect toFIG. 2,reinforcement structures406 do not pass through aninterior volume412 ofTES unit416. Instead,reinforcement structures406 comprise a trussedframework410 that is affixed along anexterior surface422 ofwall402. As such, each trussedframework410 provides structural reinforcement alongexterior surface422 ofwall402 ofTES unit416.Interior volume412, likeinterior volume212 described above with respect toFIGS. 2 and 3, contains a porous thermal storage medium therein, which is designed to retain heat from the compressed air passing throughTES unit416.
• FIG. 5 illustrates a cross-sectional view ofTES unit416. As can be seen inFIG. 5, trussedframework410 comprises a plurality ofrods414 affixed to a plurality ofanchors418, the plurality ofrods414 being further affixed to and bounded by arim420.Anchors418 may be affixed to wall402 through any known means, such as by bolt or by weld.Rods414 andrim420 may be made of steel, but are not limited as such, and may be made of any suitable material.Rods414 are arranged betweenanchors418 andrim420 to form the trussed framework about the external surface ofwall402. It is to be appreciated that the precise number ofrods414 and anchors418 used is not imperative to the invention, but the number ofrods414 and anchors418 utilized should be of an amount sufficient to allow the trussed framework to pressurizewall402.
• Using the trussedframework410 as described above with respect to the embodiment shown inFIGS. 4 and 5, wall stresses caused by high air pressure withinwall402 can be substantially relieved, thereby allowingwall402 to have a thickness substantially less than that of conventional TES units. Reduced wall thickness acts to mitigate the substantial thermal stresses present in pressure vessels, thermal stresses that become more prevalent as the walls become thicker. As an additional benefit,TES unit416 may be both easier and less expensive to construct and transport than conventional TES units.
• Next,FIG. 6 illustrates yet another embodiment of the present invention.FIG. 6 is a cross-sectional view ofTES unit516, which combines the concepts of the spoke-shaped reinforcement structure ofTES unit116 shown inFIGS. 2,3 with the external trussed framework ofTES unit416 shown inFIGS. 4,5. In particular,TES unit516 comprises a plurality ofrods510 configured to pass through both awall502 and aninterior volume512, forming a spoke-shaped framework withininterior volume512.Rods510 are fixedly attached to the outer surface ofwall502 byanchors518 and are coupled at acommon centerpoint hub522 located withininterior volume512.TES unit516 further includes a trussedframework524 disposed about an outside surface ofwall502. The trussedframework524 comprises a plurality ofrods514 affixed to theanchors518, the plurality ofrods414 being further affixed to and bounded by arim520.Rods514 are arranged betweenanchors518 andrim520 to form the trussed framework about the outside surface ofwall502.
• As can be readily appreciated, the combination of the spoke-shaped reinforcement structure and the external trussed framework shown inFIG. 6 provideswall502 with substantial protection from pressure-related stresses using walls that are thinner than walls of conventional TES units. Accordingly,TES unit516, likeTES unit116 andTES unit416 described above, can be constructed to have thinner walls than conventional TES units, thereby reducing the cost and complexity of constructing the TES unit, and further reducing the likelihood of thermal stresses being suffered throughout regular operation of the ACAES system.
• Therefore, according to one embodiment of the invention, a thermal energy storage system is disclosed, the thermal energy storage system comprising a pressure vessel configured to withstand a first pressure, wherein the pressure vessel has a wall comprising an outer surface and an inner surface surrounding an interior volume of the pressure vessel. The interior volume of the pressure vessel has a first end in fluid communication with one or more compressors and one or more turbines, and a second end in fluid communication with at least one compressed air storage component. A thermal storage medium is positioned in the interior volume, and at least one reinforcement structure is affixed to the outer surface of the wall, wherein the at least one reinforcement structure configured to reinforce the wall to withstand a second pressure greater than the first pressure.
• According to another embodiment of the invention, a method of forming a thermal energy storage pressure vessel is described. The method comprises forming a wall having a predetermined height and thickness, wherein an inner surface of the wall bounds an interior volume therein. The method further comprises affixing a reinforcement structure to a surface of the wall at a first location, affixing at least one additional reinforcement structure to a surface of the wall at another location along the height of the wall, and disposing a porous thermal storage medium within the interior volume.
• According to yet another embodiment of the invention, a thermal energy storage pressure vessel is disclosed, the thermal energy storage pressure vessel comprising a concrete cylindrical wall bounding an interior volume, wherein the interior volume is configured to allow air passage therethrough, and at least one reinforcing structure affixed to an outer surface of the concrete cylindrical wall. The thermal energy storage pressure vessel further comprises a porous thermal matrix material disposed within the interior volume of the concrete cylindrical wall, wherein the porous thermal matrix material is configured to allow air passage therethrough.
• This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claims (20)

1. A thermal energy storage system comprising:

a pressure vessel configured to withstand a first pressure, the pressure vessel having a wall comprising:

an outer surface; and

an inner surface surrounding an interior volume of the pressure vessel, the interior volume having:

a first end in fluid communication with one or more compressors and one or more turbines; and

a second end in fluid communication with at least one compressed air storage component;

a thermal storage medium positioned in the interior volume; and

at least one reinforcement structure affixed to the outer surface of the wall; the at least one reinforcement structure configured to reinforce the wall to withstand a second pressure greater than the first pressure.

2. The thermal energy storage system ofclaim 1 wherein the at least one reinforcement structure comprises a plurality of steel rods interconnected to form a trussed framework about the outer surface of the wall.

3. The thermal energy storage system ofclaim 2 further comprising a steel rim disposed about an outer circumference of the trussed framework.

4. The thermal energy storage system ofclaim 1 wherein the at least one reinforcement structure extends into the interior volume of the pressure vessel.

5. The thermal energy storage system ofclaim 4 wherein the at least one reinforcement structure comprises a plurality of steel rods forming a spoke-shaped framework within the interior volume of the pressure vessel.

6. The thermal energy storage system ofclaim 1 wherein the at least one reinforcement structure comprises:

a plurality of first rods interconnected between a plurality of wall-mounted anchors and a circumferential rim to form a trussed framework about the outer surface of the wall; and

a plurality of second rods forming a spoke-shaped framework within the interior volume of the pressure vessel.

7. The thermal energy storage system ofclaim 1 wherein the at least one reinforcement structure comprises a plurality of reinforcement structures disposed along a length of the pressure vessel.

8. The thermal energy storage system ofclaim 1 wherein the wall of the pressure vessel is formed of concrete.

9. The thermal energy storage system ofclaim 1 wherein the thermal storage medium is a porous thermal storage medium disposed within the interior volume of the pressure vessel.

10. The thermal energy storage system ofclaim 9 wherein the porous thermal storage medium comprises at least one of natural stone, ceramic, concrete, cast iron, nitrate salt, and mineral oil.

11. The thermal energy storage system ofclaim 1 wherein the pressure vessel is cylindrical in shape.

12. A method of forming a thermal energy storage pressure vessel, the method comprising:

forming a wall having a predetermined height and thickness, wherein an inner surface of the wall bounds an interior volume therein;

affixing a reinforcement structure to a surface of the wall at a first location;

affixing at least one additional reinforcement structure to a surface of the wall at another location along the height of the wall; and

disposing a porous thermal storage medium within the interior volume.

13. The method ofclaim 12 wherein the affixing of a reinforcement structure to the surface of the wall comprises:

affixing a plurality of anchors to an outside surface of the wall;

attaching a plurality of rods to the anchors at a first end of the rods; and

attaching the plurality of rods to a rim at a second end of the rods such that the plurality of anchors, the plurality of rods, and the rim form a trussed framework about an outside surface of the wall.

14. The method ofclaim 12 wherein affixing the reinforcement structure to the surface of the wall comprises:

affixing a plurality of anchors to an outside surface of the wall; and

affixing a plurality of rods to the plurality of anchors, the plurality of rods passing through the wall to form a spoke-shaped framework within the interior volume of the wall.

15. The method ofclaim 12 wherein affixing the reinforcement structure to the surface of the wall comprises:

affixing a plurality of anchors to an outside surface of the wall;

attaching a plurality of first rods to the anchors at a first end of the first rods;

attaching the plurality of first rods to a rim at a second end of the first rods such that the plurality of anchors, plurality of first rods, and the rim form a trussed framework about an outside surface of the wall; and

affixing a plurality of second rods to the plurality of anchors, the plurality of second rods passing through the wall to form a spoke-shaped framework within the interior volume of the wall.

16. A thermal energy storage pressure vessel comprising:

a concrete cylindrical wall bounding an interior volume, wherein the interior volume is configured to allow air passage therethrough;

at least one reinforcing structure affixed to an outer surface of the concrete cylindrical wall; and

a porous thermal matrix material disposed within the interior volume of the concrete cylindrical wall, wherein the porous thermal matrix material is configured to allow air passage therethrough.

17. The thermal energy storage pressure vessel ofclaim 16 wherein the at least one reinforcing structure comprises a steel ring and a plurality of trusses interconnected to form a framework about the outer surface of the concrete cylindrical wall.

18. The thermal energy storage pressure vessel ofclaim 16 wherein the at least one reinforcing structure extends into the inner volume of the concrete cylindrical wall.

19. The thermal energy storage pressure vessel ofclaim 18 wherein the at least one reinforcing structure comprises a plurality of interconnected steel rods affixed at a common centerpoint within the inner volume of the concrete cylindrical wall.

20. The thermal energy storage pressure vessel ofclaim 16 wherein the at least one reinforcing structure is secured to the outer surface of the concrete cylindrical wall by a plurality of anchors.

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