BRPI0913767A2 - coaxial gas storage system by compression and adsorption - Google Patents

Abstract

COAXIAL GAS STORAGE SYSTEM BY COMPRESSION AND ADSORPTION. THE COAXIAL SYSTEM AND GAS STORAGE BY COMPRESSION AND ADSORPTION. It has application in the area of fuels, in particular, for gas storage and transport. The present invention develops optimized gas storage operations, using the energetic combination of simultaneous adsorption and desorption effects in a new compression gas storage system. and adsorption, consisting of two concentric reservoirs with equal loads of activated carbon. The gas loading and unloading system presented does not make use of accessory means, such as external sources, and has greater thermal stability in a reasonable pressure range, that is, it is more efficient and allows new storage cycles without external treatments resulting in a cost of lower operation when compared to the current state of the art.

Description

COAXIAL GAS STORAGE SYSTEM BY

COMPRESSION AND ADSORPTION

Field of the Invention

The present invention has application in the field of fuels, especially for gas storage and transport.

Gas storage in the proposed system could be applied in automobiles, in industries whose energy matrix is natural gas, or in any establishment whose need for storing gas for later use is present (hospitals, shopping malls, air conditioning systems, gas stations). fuels and the like). Applications are possible on smaller or larger scales (automobiles, hospitals, industries, air conditioning plants, gas stations) by adapting the corresponding dimensions of the coaxial system.

summary

The present invention relates to a compression and adsorption natural gas storage system utilizing the energies inherent in the gas loading and unloading steps. It deals in particular with the development of a compression and adsorption natural gas storage system using the energetic combination of the adsorptive and desortive effects of simultaneous loading and unloading, respectively.

Priorities

Natural gas storage through the Compressed Natural Gas (CNG) process, under pressures of up to 200 bar at room temperature, is the way currently used to achieve energy density per unit volume of the storage tank, suitable for its storage. use as fuel. The use of high pressure levels makes the operating cost in multi-stage compression stations for gas loading high. CNG storage relies on the use of cylinders as reservoirs, which must be made of sturdy material of compatible wall thickness, requiring ample physical space for the storage tank. Adsorbed natural gas (GNA) technology, in which gas is stored primarily as adsorbed in a porous solid under moderate pressures (35 to 40 bar) (LOZANO-CASTELLÓ, D .; ALCANIZ-MONGE, J .; DE LA CASA-LILLO, A. A. CAZORLA-AMORÓS, D .; LINARES-SOLANO, Av Advances in the study of methane storage in porous carbonaceous materials. Fuelf 81, 1777-1803, 2002b.), Is the largest alternative potential for substitution of the CNG process.

In this way, it is expected to reduce the operational expenses inherent to the loading process, also allowing the flexibility of fuel tank configuration and increasing the security of the storage system.

Developments of the natural gas storage process with arisorbent (adsorbed natural gas - GNA) have been undertaken (CHANG, K. JV TALU, O., Behavior and experimental performance of natural gas storage cylinders during discharge. Appfied Thermal Engineering, 16, 5, 359-374, 1996; Vasiliev, L.L. KANONCHIK, LE; MISHKINIS, DA; RABETSKY, M.L., Adsorbed natural gas storage and transportation vessels.International Journal of Thermal Science, 39, 1047-1055, 2000; BILOÉ, S.; GGETZ, V .; MAURAN, Sv Dynamic discharge and performance of an adsorbent nevv for natural gas storage.AIChE Journal, 47, 12, 2819-2830, 2001; Yang, XD; ZHENG, QR; GU, AZ LU, X. Sv Experimental studies of the performance of adsorbed natural gas storage system during discharge Applied Thermal Engineering, 25, 591 - 601, 2005; LEE, JW, BALATHANIGAIMANI, MSv KANG HC, SHIM, WG, KIM Cv MOON, Journal of Chemical and Engineering Date 52 (1): 66-70 JAN-FEB 2007), characterized by CNG process improvements.

The aim of GNA process operations is to obtain a higher adsorbed amount of gas in the system loading stage and a greater availability in the discharge stage. Indications from experimental methane gas evaluations (Chang and Talu, 1996 cited above) have shown practical difficulties in operating a GMA system under isothermal conditions. Temperature variations in adsorptive charge and desortive discharge promote decreases in process efficiency.

Operations with control of the flow of feed and release of gas in the storage system and the use of thermostatic devices have been proposed (Biloé et al., 2001; Yang et. Al., 2005; Lee et. Al., 2007). ensure lower energy wraps ensuring more operational stability. Different types of activated charcoal have been used, operating within a pressure range of 0.1-100 MPa (Vasilev et al., 2000).

Operations of the natural gas storage process by adsorption were performed by Mota (MOTA, J. B. B, Impact of gas composition on natural gas storage by adsorption. AIChE Journal, 45, 5, 986-996, 1999) using natural gas that served to evaluate the performance of the system subjected to the adsorption of the real hydrocarbon mixture of NG (ethane, propane, n-butane and n-pentane). It was evidenced that the heavier components than methane had higher adsorption selectivity in the activated carbon bed after the discharge process, causing greater retention of the predominant methane component in the NG.

Biloé et. al. (2001 - cited above) investigated the influence of two different heat exchange conditions external to the walls of a storage cylinder, using an outer jacket. The first used water as a refrigerant and the second employed air. In both cases the flow rate was 4 NL / min used for each fluid. The temperature measured in the inner wall of the cylinder indicated a decrease of 35 K and 1.5 K for air and water circulation, respectively. The authors concluded that with water circulation there would be a higher thermal stability in the adsorptive system. Yang et. there. (2005) installed a "U" pipe in the central region of an adsorbed natural gas storage cylinder, represented by methane, with the interest of supplying heat to the system during the discharge step, to take advantage of the cooling water of the methane. combustion system of a vehicle, reaching a temperature in the range of 343 K to 353 K. As a result of the discharge experiments performed with and without heating water at 343 K, the authors could conclude that the temperature drop without circulating water was 37 K and with heating water was only 3.2 K, achieving better efficiency with regard to methane availability to the system during discharge.

Lee et al ', 2007) studied the influence of temperature on activated charcoal adsorbent beds, types RP-15 and RP-20, with high surface areas. They operated in a 0.5 L capacity storage cylinder with loading pressures of approximately 35 bar. Operations were conducted at temperatures of 293 K, 303 K and 313 K. As a result, the authors obtained higher Lirna adsorbed methane at a lower circulation temperature (293 K).

Prior Art Problems and Limitations

Operations of the natural gas storage process by compression and adsorption have been applied in systems installed with laboratory and pilot scale activated carbon porous bed.

In such systems, due to the conduct of operations, problems occur mainly with values of the following parameters: feed flow, discharge flow, working pressure and number of storage cycles without bed regeneration. The resulting problems are directly associated with the temperature reached in the storage bed, due to the adsorption and desorption energies respectively released or absorbed in the system loading and unloading stages. Researchers highlight problems arising from cyclical gas storage operations. Chang and Talu (1996 - cited above) observed that the natural gas loading cycle in the storage reservoir for vehicular use would not be the limiting step of GNA technology, since the loading could be carried out at filling stations equipped with an exchange system. heat or under very slow, overnight feeding conditions to dissipate the adsorption heat. The problem would be discharge due to the impact of the desorption heat involved in this step. The authors concluded that the operation of a GNA system is not executable under isothermal conditions, ie under any actual discharge flow there will be a corresponding temperature drop. For the smallest discharge flow rate employed in their experiments (li) L / min), there was a temperature drop of 5 K and an adsorptive capacity of about 8%, defined as the ratio between the amount of methane released under normal conditions. over the amount released in an isothermal process, At the highest discharge flow (15 L / min), the temperature drop was 37 K and there was a 29% capacity loss.

In short, temperature variations in the adsorptive charge and in the dorsive discharge promote decreases in process efficiency.

Vrisiev et al (2000 - cited above) stated that there is a similarity between the desorption and adsorption processes. In the first process there would be greater efficiency if there was a heat source in the porous bed, while in the second case in the adsorption process there should be a heat removal from the bed. In this direction, the authors focused on desorption of methane with heat supply to the activated carbon sample using an electric heater positioned on the sample axis contained in the storage cylinder.

Tanger et al (2003), holders of US Patent No. 6613126 B2, proposed a methodology for storage of natural gas by adsorption in a two-tank structured system previously involving the separation of low molecular weight gas components (methane, ethane). in one reservoir, and in the other reservoir those components with the most carbon numbers (propane, butane,.). The method claims the solution of the problem caused in natural gas storage adsorptive systems, where the higher carbon number components condense inside the pores of the adsorbent, inhibiting the adsorption of the main component of natural gas.

In the method it was proposed that the lighter components be stored under higher pressures while the heavier hydrocarbons were subjected to higher pressures. »The thermal effects were not considered, and the effects involved when desorption Mo second reservoir were not sought. adsorption of heavier ones is increased by cooling this part of the system. The use of an external source of heat removal distinguishes the proposition of the aforementioned authors (Tanger et al., 2003) of the present claim that does not apply external source, choosing to involve the coaxial gas storage system, making use of the energies. adsorption and desorption associated with gas loading and unloading operations,

Thus Vasilev et al. (2000 - cited above) regarding Tanger et; a! = (2003), US Patent No. 6613126 B2 holders use external devices in their solutions.

Kobayash! et al. (1994) patented a method according to the proposition that indicated the treatment of a gas mixture to separate the components by selective adsorption. The method places the invention as capable of improving the separation of the components of a gas, containing with the contribution of preferential desorption of one of the components, favoring the separation of the other components that remained adsorbed. The system did not resort to the associated effects of adsorption and desorption in the operation performed, being of completely different concept from that applied to the coaxial gas storage system, object of the present claim.

Pupier et al. (2005 - cited above) evaluated the effects of cyclic natural gas loading and unloading operations on a 2 L capacity storage cylinder containing an activated carbon adsorbent composite and expanded natural graphite. After the first cycle, successive loading and unloading cycles were performed without?. bed regeneration. For the cyclic operations with natural gas, it was observed that the transient profiles of pressure, temperature and flow fed were influenced by the number of cycles. The efficiency of the storage process, defined as the relationship between the volumetric availability of natural gas in cycle number η and this availability for the first cycle, was also strongly dependent on the number of cycles. This was due to preferential adsorption and saturation of the adsorbent paio? hydrocarbons heavier than methane and also carbon dioxide, both present in natural gas.

Ridha et al. (2007 - cited above) studied the influence of discharge flow from a storage cylinder containing activated charcoal, zeolites or silica gel with the volumetric availability of methane to the system. Evaluations showed increases in flow between 1 L / min to 5 L / min, which promoted a reduction in volumetric availability for the system by 7.6 to 12.1%. Additionally, volumetric availability was evaluated for ethane and propane gases, for which there was a reduction of 14.98%, and 14.54%, respectively, for the same flow range. Such reductions in volumetric availability occurred due to the influence of temperature in the discharge process As the discharge rate increased, the effects of temperature were more severe, increasing thermal instability, making it difficult to release gas from the bed.

The use of high pressure levels is also a problem that occurs and makes the operating cost of multi-stage compression stations for gas loading high. In addition, CNG storage relies on the use of cylinders as reservoirs, which must be made of tough material of compatible wall thickness, requiring ample physical space for the storage tank.

Objectives of the Invention

The object of the present invention is to provide a gas charging and discharging system which does not make use of ancillary means such as external sources, which has greater thermal stability over a reasonable pressure range, that is, is more efficient, and allows new storage cycles without external treatments resulting in lower operating cost compared to the current state of the art.

Solution

The system to which the present invention relates considers the losses of gas adsorptive storage efficiency resulting from temperature elevations in the loading step; and gas release reductions due to temperature decreases in the discharge stage; as a consequence of the exothermic and endothermic effects, respectively involved in adsorption and desorption. There is no use of accessory means, such as external thermal sources, taking advantage of the energies inherent to the mentioned steps.

As a solution for the implementation of the system, a storage system has been developed which has as its principle the utilization of the adsorption and desorption energies released or absorbed by the adsorbent bed during the loading and unloading stages.

Using the energetic combination of the adsorption and desorption effects, an adsorption natural gas storage system consisting of two concentric reservoirs with equal charges of activated carbon (coaxial system) was designed. Through the heat exchange between the internal and external reservoirs of the system with coaxial activated carbon beds, a storage operation is performed, operating simultaneous methane loading and unloading steps. From one operating cycle to another, the loading and unloading stages alternate between the inner and outer reservoirs, respectively.

Benefits

The system coax! Gas storage when compared to a traditional system, which consists of only one storage cylinder, is more thermally stable, according to the bed temperature evolution, more thermally stable before all the loading and unloading flows used. from 1.15 L / min to 9.09 L / min for all working pressures employed in a range of 10 bar to 60 bar.

Results for adsorbed quantities for coaxia! developed storage, show an increase of about 50% adsorbed methane mass when compared to the traditional system, under the same operating conditions.

From the iTiedscfes compared pressure, between the heat exchange systems (system with coaxia system!) And traditional, in the discharge step 3 a constant flow, it turns out that it is possible to promote! removal of all gas stored in the coaxial system, caused by the bed gas desorption. In this case, natural bed regeneration occurs, thus allowing new storage cycles without external treatments, which reduces operating costs and increases process efficiency.

In summary, the present invention provides a gas charge and flow system that does not make use of accessory means such as external sources; It has greater thermal stability over a reasonable pressure range, ie it is more efficient; and allows new storage cycles without external treatments resulting in lower operating cost compared to the current state of the art.

Detailed Description

The system is a thermally insulated storage reservoir on its outer wall consisting of two coaxial cylinders of equal volume, each containing the same mass of charcoal filled to fill its entire volume. The important thing is that the adsorbent bed of the outer cylinder is disposed anefarly surrounding the inner cylinder of the system.

The cylinders, when in natural gas storage operation, are fed with this gas alternately (internal, external) and discharged with the gas alternately (external, internal) at the same time, in order to have simultaneous occurrences with adsorption effects. and gas desorption, respectively, in feed and discharge.

Compounding a cycle, the charging process consists of supplying gas to the internal cylinder under constant flow to a certain loading pressure which, when reached, has interrupted the flow rate. At the same time, the discharge process consists of releasing the gas from the outer cylinder at a constant flow rate until the proper gauge pressure is reached, eg 0.1 bar.

In this first cycle the processes of loading and unloading are carried out simultaneously and respectively in the internal and external cylinders of sr: rteyra, in exothermic and endothermic forms, due to the adsorption and desorption capacitors.

The coaxial system allows an energy exchange through the non-insulated wall of the inner cylinder, thereby promoting a reduction in temperature, which favors the adsorption and additional storage of gas, while promoting in the outer cylinder an increase in temperature, which favors the desorption of gas and sub, such ccr.peta release. In a second cycle, the operation occurs alternately, feeding the gas in the outer cylinder and releasing it from the inner cylinder, where it was stored. The thermal flow through the inner cylinder wall occurs inversely from the outer cylinder to the inner cylinder,

The invention can be used for any gas that is part of the mixture of natural gas components (methane, ethane and propane), but other gases in need of storage and susceptible to adsorption on solids can be used.

hydrogen, carbon oxyels and the like). Implementation

To realize the system of the invention it is necessary:

A coaxial set of cylinders (inner cylinder and outer cylinder), made with any goal! resistant to operating pressures, with the inner cylinder and outer cylinder having equal volumes and the same activated carbon mass filling their volumes. The important thing is that the adsorbent bed of the outer cylinder is arranged in a yearning surrounding the inner cylinder of the system;

For isoating material positioned on the inner wall of the outer cylinder;

- Metal pipes and fittings for alternate loading operations c: cylinder discharge;

To perform measurements of interest one can complete the system of the invention with;

Temperature gauge thermocouples, positioned in the centered region of the inner cylinder and in the annular region between the inner and outer cylinders; - Pressure transducers installed on top of inner and outer cylinders for pressure measurements;

These last two devices are not required for proper system operation.

Description of Figure 1

Operation; CirJo 1

Internal cylinder supply (1) via internal cylinder supply and discharge valve (5) and internal cylinder gas diffuser (3), with pressure and temperature increase measurement by pressure transducer and temperature indicator (7) .

Discharge of the outer cylinder (2) by the external cylinder supply and discharge valve (6) and gas diffuser in the outer cylinder (4), with pressure and temperature reduction measurement by the pressure transducer and temperature indicator (7).

Heat flow from inner cylinder (1) to outer cylinder (2).

Conclusion of the operation: inner cylinder (1) loaded and outer cylinder (2) discharged.

Operation- Ice 2

External cylinder supply (2) through external cylinder supply and discharge valve (6) and external cylinder gas diffuser (4), with pressure and temperature increase measurement oefo pressure transducer and temperature indicator (7) .

Drop cylinder 1 from inner cylinder (1) via inner cylinder feed and discharge valve (5) and gas diffuser in diin-rj: inner (3), with pressure and temperature reduction measurement by pressure transducer and temperature indicator (7). Bottom flow from outer cylinder (2) to inner cylinder (1).

Conclusion of operation: external cylinder (2) loaded and internal cylinder (1) discharged.

Construction Example

As a non-limiting embodiment of the invention, the inner cylinder is constructed of 304 stainless steel with a structure compatible with the inner space of the outer cylinder, having a usable volume of 500 cm3 with a height of approximately 22 cm and an internal diameter of 4 cm.

The 304 stainless steel outer cylinder has a working volume of -2000 cm3, with a height of approximately 26 cm and internal diameter d3 10cm.

The insulating material, a PVC pipe with a height of 26 cm and an external diameter of approximately 10 cm is placed on the inner wall and the outer cylinder.

For alternate loading and unloading operations of the inner and outer cylinders of the coaxial system, stainless steel pipes and fittings were used.

Two thermocouple temperature gauges were positioned in the central regions of the inner and annular cylinder bed, between the inner and outer cylinders.

Pressure measurements can be made through the pressure transducer by urging on the top of the inner and outer coaxial storage cylinders.

Coaxial cylinders, when in natural gas storage operation, are charged alternately (internally or externally) and discharged alternately (externally, internally) simultaneously, so as to have the occurrences of the effects of gas adsorption and desorption, respectively on the load. and in the discharge »The energetic utilization of the energies involved in the adsorption and desorption processes is provided, through thermal exchange through the inner cylinder wall.

Operational optimizations of the natural gas compression and adsorption storage system, represented by methane, were implemented with the advent of the compression / adsorption and decompression / desorption coaxial natural gas storage system which operated in simultaneous stages of loading and unloading sm c Coaxial syndromes, using the heat exchange of the energies involved in the effects of adsorption and desorption.

Temperature measurements at the loading stage indicated that the coaxial system remains more stable (constant temperature) in the adsorption process when compared to the traditional adsorption storage system.

When compared, the pressure measurements of the heat exchange system (coaxial system) and the traditional system, those of the invention show that the equilibrium pressure is reached faster.

Results regarding the amount of adsorbed gas show an increase in methane adsorbed mass of about 50%, when compared to the traditional storage system, at a pressure of 60 bar, at a flow rate of 9.09 L / min.

Regarding the volumetric storage capacity, a gain of about 28% by volume was found for the ccaxte! when compared to the traditional one.

Pressure changes in the heat-exchanging coaxial system highlight the potential for complete regeneration of the activated carbon bed by desorption of all stored gas, which decreases the cost of the process and increases its efficiency.

Claims (10)

1. COMPRESSION AND ADSORPTION COAXIAL GAS STORAGE SYSTEM composed of an insulating material, pipes, fittings, activated carbon and two cylinders, one inner and one outer, characterized in that the adsorbent bed of said outer cylinder is annularly surrounded by said one. inner cylinder and cylinders are coaxial and concentric. Coaxial Compression and Adsorption Gas Storage System according to Claim 1, characterized in that said cylinders have equal volumes and contain the same mass of activated carbon completely filling their volumes. COAXIAL COMPRESSION AND ADSORPTION GAS STORAGE SYSTEM according to claim 1 or 2, characterized in that said cylinders are made of any metal resistant to operating pressures. COAXIAL COMPRESSION AND ADSORPTION GAS STORAGE SYSTEM according to claim 1, 2 or 3, characterized in that the insulating material is positioned on the inner wall of the outer cylinder. Coaxial Compression and Adsorption Gas Storage System according to Claim 3 or 4, characterized in that said cylinders are made of 304 stainless steel. Coaxial Compression and Adsorption Gas Storage System according to claim 1, 2, 3, 4 or 5, characterized in that said inner cylinder has a structure compatible with the inner space of the outer cylinder. Coaxial Compression and Adsorption Gas Storage System according to Claim 6, characterized in that said inner cylinder has a working volume of 300 to 700cm3, has a height of 18 to 22 cm and an internal diameter of 2 to 6 cm. Coaxial Compression and Adsorption Gas Storage System according to Claim 6 or 7, characterized in that said external cylinder has a working volume of 1500 to 2500cm3, has a height of 20 to 32 cm and an internal diameter of 4 to 16 cm. Coaxial Compression and Adsorption Gas Storage System according to Claim 4, 5, 6, 7 or 8, characterized in that the insulating material has a height of 20 to 32 cm and an external diameter of 5 to 15 cm. COAXIAL COMPRESSION AND ADSORPTION GAS STORAGE SYSTEM according to claims 4, 5, 6, 7, 8 and 9, characterized in that the inner cylinder has a working volume of 500 cm3, a height of 22 cm and an internal diameter of 4 cm; the outer cylinder has a usable volume of -2000 cm3, a height of 26 cm and an inner diameter of 10 cm; and the insulating material has a height of 26 cm and an outside diameter of 10 cm.