WO2010115256A1 - Coaxial gas storage system by compression and adsorption - Google Patents

Abstract

A gas storage system by compression and adsorption is useful in the field of fuels, in particular for storing and transporting gas. The present invention optimises gas storage operations by utilizing the energy obtained by the combination of the effects of simultaneous adsorption and desorption in a new gas storage system by compression and adsorption comprising two concentric reservoirs containing identical charges of activated carbon. The present gas charging and discharging system does not use auxiliary means, such as external sources, and has an increased thermal stability in a reasonable pressure range, i.e. it is more efficient and makes new storage cycles without external processing possible, reducing operating costs in comparison with the prior art.

Description

 COAXIAL GAS STORAGE SYSTEM BY

 COMPRESSION AND ADSORPTION

Field of the Invention

The present invention has application in the field of fuels, in particular 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 uses cylinders as reservoirs,

5 which must be made of tough 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 to a porous solid under moderate pressures (35 to 40

10 bar) (LOZANO-CASTELLÓ, D .; ALCANIZ-MONGE, 1; DE LA CA5A-LILLO, MA; CAZORLA-AMORÓS, D.; LINARES-SOLANO, A., Advances in the study of methane storage in porous carbonaceous materials Fuel, 81, 1777-1803, 2002b.), Is the most potential alternative for replacement of the CNG process.

i s This way, we expect 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 adsorbent (adsorbed natural gas - GNA) have been undertaken (CHANG, KJ; TALU, O., Behavior and experimental performance of natural gas storage cylinders during discharge. Applied Thermal Engineering, 16, 5, 359-374, 1996; VASIUEV, L.L. KANONCHIK, LE; MISHKINIS, DA; RABETSKY, 5 MI, Adsorbed natural gas storage and transportation vessels.

 International Journal of Thermal Science, 39, 1047-1055, 2000; BILOÉ, S .; GOETZ, V .; MAU RAN, S., Dynamic discharge and performance of a new adsorbent for natural gas storage. AIChE Journal, 47, 12, 2819-2830, 2001; YANG, X. D .; ZHENG, Q. R .; GU,

30 A. Z .; LU, X. S., Experimental studies of the performance of adsorbed natural gas storage system during discharge. Applied Thermal Engineering, 25, 591-601, 2005; LEE, J.W., BALATHANIGAIMANI, S., KANG H.C., SHIM, W.G., KIM C, MOON, H., Journal of Chemical and Engineering Date 52 (1): 66-70 JAN-

35 FEB 2007), featuring improvements concerning the CNG processes.

The aim of GNA process operations is to obtain a higher adsorbed amount of gas at the system loading stage and a higher greater availability at the unloading stage. Indications from experimental methane gas evaluations (Chang and Talu, 1996 cited above) have shown practical difficulties in operating a GNA 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 at a pressure range of the order of 0.1-100 MPa (Vasilev et al. 2000).

Natural gas storage process operations by adsorption were performed by Mota (MOTA, JP B, Impact of gas composition on natural gas storage by adsorption. AIChE Journal, 45, 5, 986-996, 1999) using natural gas that It served to evaluate the performance of the system subjected to adsorption of the real mixture of NG hydrocarbons (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. al. (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, for that they took 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 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 a higher adsorbed amount of methane at a lower circulation temperature (293K).

Prior Art Problems and Limitations

Compression and adsorption natural gas storage process operations have been applied in laboratory and pilot scale activated carbon porous bed systems.

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 feed ovemight 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 lowest discharge flow rate employed in their experiments (1.0 L / min), there was a 5 K drop in temperature and a loss in adsorptive capacity of about 8%, defined as the ratio between the amount of methane released under real conditions. about the amount released in an isothermal process. For the highest discharge flow (15 L / min), the temperature drop was 37 K and there was a 29% capacity loss.

In summary, temperature variations in adsorptive charge and desortive discharge promote decreases in process efficiency.

Vasilev 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 methodology for storage of natural gas by adsorption in a two-tank structured system previously involving the separation of gas components of low molecular mass (methane, ethane) in one reservoir, and in the other reservoir those components of higher carbon numbers (propane, butane, ..) ■ The method claims the solution of the This problem is caused in adsorptive natural gas storage 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 lighter components be stored under higher pressures while heavier hydrocarbons were subjected to higher pressures. The thermal effects were not considered, as well as the effects involved during desorption. In the second reservoir it was sought to increase the adsorption of the heavier by cooling this part of the system. The use of an external source of heat removal distinguishes the proposition of the mentioned authors (Tanger et al., 2003) of the present claim, which 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, both Vasilev et al. (2000 - quoted above) as

Tanger et al. (2003), US Patent No. 6613126 B2 use external devices in their solutions.

Kobayashi 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, 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. 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 ratio of volumetric availability of natural gas in cycle number n to availability in the first cycle, was also strongly dependent on number of cycles. This was due to the preferential adsorption and saturation of the adsorbent by hydrocarbons heavier than methane and also by 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. The evaluations showed flow increases 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 availabilities were 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 on 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 in 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.

OBJECTS OF THE INVENTION The object of the present invention is to provide a gas charging and discharging system which does not make use of accessory means such as external sources, which has a higher thermal stability over a reasonable pressure range, that is, is more efficient. and allowing 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 was developed that 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 reservoirs was designed. concentrics bearing equal loads of activated carbon (coaxial system). 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 coaxial gas storage system 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 in relation to all load flows and discharge rates, 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 regarding the adsorbed quantities, for the developed coaxial storage system, show an increase of about 50% of adsorbed methane mass when compared to the traditional system, under the same operating conditions. From the comparative pressure measurements between the systems with heat exchange (system with coaxial system) and the traditional, at the discharge stage at a constant flow, it is possible to promote the 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 loading and unloading system which does not make use of accessory means such as external sources; has greater thermal stability over a reasonable pressure range, ie more efficient; and allows new storage cycles without external treatments resulting in a 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 activated carbon filling its entire volume. The important thing is that the adsorbent bed of the outer cylinder is arranged annularly 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, so as to have simultaneous occurrences of adsorption effects. and gas desorption, respectively, in feed and discharge. In one cycle, the charging process consists of supplying the gas to the inner cylinder at a constant flow rate 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 loading and unloading processes are carried out simultaneously and respectively in the internal and external cylinders of the system, exothermic and endothermic, due to the heat of adsorption and desorption.

The coaxial system allows an energy exchange through the uninsulated wall of the inner cylinder, promoting a reduction in the temperature, which favors the adsorption and the additional storage of the gas, while promoting in the outer cylinder a temperature rise, which favors the desorption of the gas and its most complete 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. Thermal flow through the inner cylinder wall occurs inversely from the outer cylinder to the inner cylinder.

The invention may 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 may be used (hydrogen gas, carbon oxides and similar).

Implementation

To realize the system of the invention it is necessary:

- A coaxial set of cylinders (inner cylinder and outer cylinder), made of any metal resistant to operating pressures, with the inner cylinder and outer cylinder having equal volumes and the same mass of activated carbon filling their volumes. What is important is that the adsorbent bed of the outer cylinder is annularly arranged around the inner cylinder of the system;

- An insulating material positioned on the inner wall of the outer cylinder;

- Metal pipes and fittings for alternate cylinder loading and unloading operations;

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

- Temperature measuring thermocouples, positioned in the central region of the inner cylinder bed 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: Cycle 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) .

 External cylinder discharge (2) by external cylinder supply and discharge valve (6) and external cylinder gas diffuser (4), with pressure and temperature reduction measurement by 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: Cycle 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 by pressure transducer and temperature indicator

THE).

Discharge of cylinder 1 from inner cylinder (1) via internal cylinder feed and discharge valve (5) and gas diffuser into inner cylinder (3), with pressure and temperature reduction measurement by pressure transducer and temperature indicator (7). Heat flow from outer cylinder (2) to inner cylinder

(D-

Conclusion of operation: external cylinder (2) loaded and 5 internal cylinder (1) discharged.

Construction Example

As a non-limiting example of the implementation 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 cm ³ with a height of approximately 22 cm and an internal diameter of 4 cm. cm. is The 304 stainless steel outer cylinder has a useful volume of

2000 cm ³ , with a height of approximately 26 cm and an internal diameter of 10 cm.

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

For alternate loading and unloading operations of the internal and external cylinders of the coaxial system, 25 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.

 30

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

35 Coaxial cylinders, when in storage operation of natural gas, are charged alternately (internal or external) and discharged alternately (external, internal) simultaneously, so as to have the occurrences of the effects of gas adsorption and desorption, respectively at loading and unloading. 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 loading and unloading stages in coaxial cylinders, using the thermal exchange of the energies involved to 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 more quickly.

Results regarding the amount of adsorbed gas show an increase in adsorbed methane 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, it was found a gain of about 28% in volume for the coaxial system when compared to the traditional one.

Pressure changes in the heat exchange coaxial system highlight the possibility of 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

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 usable volume of 300 to 700cm ³ , 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 outer cylinder has a working volume of 1500 to 2500cm ³ , 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 cm ³ , a height of 22 cm and an internal diameter of 4 cm; the outer cylinder has a usable volume of 2000 cm ³ , 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.