WORKING FLUIDS

Abstract: Method and apparatus for providing a work performing device with a working fluid, e.g. carbon dioxide, at a given temperature and pressure, in which the fluid at a lower temperature and pressure is exposed to a sorbent material, e.g. a dehydrated zeolite, which is subsequently heated at constant volume to provide the working fluid. The method may be cyclically repeated and the working fluid used to drive a turbine for the generation of electricity. A recuperative mechanism for retaining heat in the system is also described.

Description: WORKING FLUIDS The present invention relates to a method for providing a work performing device with a working fluid and in particular a working gaseous fluid, e.g. a fluid at a temperature and pressure suitable for driving a turbine for the generation of electricity, or for the movement of fluids or solids by entrainment or the enhancement of oil field recovery by inflation or pressurisation with fluids. The expression "working fluid" as used in the accompanying description of the invention includes fluids which may be said to possess a potential to do work, for example, fluids which possess a temperature and/or pressure which are thereby a potential source of energy which may be exploited to do work. By way of suitable working fluids there may be mentioned carbon dioxide (CO2), water vapour, ammonia, organic hydrocarbons, halogenated hydrocarbons and polyhalogenated hydrocarbons (PREONS), and such like, of which carbon dioxide is preferred in the temperature range 600"K to 200"K. Accordingly, the present invention provides a method for providing a work performing device with a working fluid having a temperature T U K and a pressure P bar in which the said working fluid at a temperature less than T"K and a pressure less than P bar is exposed to a sorbent material (as defined) which is subsequently heated together with the said working fluid at substantially constant volume to give the said working fluid a temperature T U K and a pressure P bar. The expression "work performing device" includes devices which inflate or increase the pressure of a region or enclosure by means of a fluid. The expression sorbent material is used to describe a range of materials that may be further described as adsorbents or persorbents. Examples of these materials and the manner in which they behave is described in ITS Patent 4 327 553- In the present invention embodiment persorbents are generally preferred and specifically there may be mentioned dehydrated zeolites and emergent adsorbents. The method of the present invention may be exploited in a cycle of events as follows. A working fluid at, e.g. ambient temperature and pressure is exposed to a sorbent material, also at ambient temperature, and allowed to reach equilibrium therewith. In this context the term "exposed" means briging together so as to allow union between the said working fluid and the said sorbent. If necessary, the pressure of the working fluid may be increased during sorption to increase the amount thereof "taken up" by the sorbent. Under these circumstances a considerable quantity of working fluid may be sorbed. The temperature of the sorbent together with the working fluid is then raised while at substantially constant volume (i.e. while the sorbent and working fluid are held in a closed environment). As the temperature rises the sorbent progressively desorbs so as to release some of the working fluid and the pressure of working fluid in the system increases. Thus, the system becomes a potential source of energy by virtue of the presence of hot, pressurised working fluid. By selecting the final temperature and pressure of the working fluid, it may be fed directly to a turbine for the generation of electricity. In doing work the temperature and pressure of the working fluid will fall, but the cycle may be repeated by exposing the working fluid to further sorbent material. It will be apparent that this whole process may be lowered in temperature range, for example, by enclosing the major artefacts of the system in a chamber which is (a) substantially insulated from the surroundings (barring any necessary supply of heat from the surroundings or rejection to the surroundings), and (b) initially ref igerating the relevant components within the chamber to the desired sub-ambient temperature, it being apparent that this initial refrigeration will only need "topping-up" relatively infrequently depending upon the imperfection of the recuperative process described in Figure 2 herein and associated text. At such a lower temperature range one would naturally seek to use a working fluid having an appropriately lower critical temperature, choosing it, for example, from the group including nitrogen, helium, neon, argon, krypton, xenon and other such like preferably-inert, so called "permanent gases". The present invention also provides apparatus for supplying a work performing device with a fluid at an elevated temperature and pressure, the apparatus comprising a source of fluid, a chamber containing a sorbent for the fluid, heating means for heating the contents of the chamber, and control means, the control means being arranged to supply, fluid from the source to the chamber for sorption by the sorbent, to retain the fluid and sorbent in the chamber and to cause the heating means to heat both fluid and sorbent while retained therein, thereby to raise the fluid to an elevated pressure and temperature, and to release the fluid at its elevated temperature and pressure from the chamber and to supply it to the work performing device. A cycle of events embodying the present invention may be described in greater detail by reference to the accompanying drawings in which Figure 1 represents diagrammatically a temperature (T)/entropy (S) cycle for a working fluid such as as C0 2 - Persorbent material, such as a dehydrated crystalline sodium alumino-silicate, in close-packed pellet or granule form, loaded into a connected series of shell and tube heat exchangers, is exposed at a temperature of 2?3°K to gaseous CO2 also at 273"K while the pressure of the CO2 is increased by, for example, conventional means from 1.1 (point F) to 60 (point B) bar. The ratio of sorbent material to CO2 by weight may conveniently be 5 to 1. The CO2 is rapidly sorbed until equilibrium is reached, with a corresponding decrease in the entropy of the CO2 and a rise in the temperature of the persorbent to approximately 300°K (point B). In this example, the amount of CO2 which is sorbed may approach 0.5 g CO2 per cc of persorbent. If the temperature of the persorbent is then increased, e.g. by heating by conventional or emergent means with a heat transfer fluid, while the persorbent and CO2 are held at substantially constant volume (i.e. within a closed environment), CO2 will be driven off from the persorbent and its pressure will rise until at a temperature of, for example 450"K, the pressure of C0 2 will have reached about 230-400 bar (point C)-_ Hot, pressurised CO2 is thus available as a working fluid, and if released through a pressure control valve, at for example 90-100 bar (point D may be made to perform work, for example by driving the blades of a turbine for generating __0V.P1 " electricity. The CO2 may continue to perform work by expansion until either its temperature and pressure fall to the cycle starting point F (273"K, for example 1.1 bar) when the cycle may be repeated, or to some point E, below 273°K, (e.g. 200 °K at 1.3 bar by means of a turbine of higher isentropic efficiency) when either the same cycle (EBCD) may be repeated starting from a lower temperature or advantage may be taken of the circumstances to operate in addition an air-conditioning stage (EF). When an air conditioning cycle is operated the (cold) CO2 is used to cool the ambient air, and as a result the temperature of the C0 2 will increase (at substantially constant pressure) until either it approaches the temperature of ambient air or is removed from the air-conditioning cycle (point F), when it may be re-introduced into the persorbent cycle BCDEFB). The combination of persorbent and air conditioning cycles may be particularly valuable in, for example, an office block, requiring both electricity and an air-conditioning system. In such an instance, persorption would normally take place during the night with desorption commencing at, e.g. 7 am, when electricity, heating and cooling are required jointly or severally. It will be appreciated that if the present invention is to be economically exploited, heat present in the desorbed sorbent material must be retained in the system, and preferably used to increase the temperature of the freshly sorbed material. This may be achieved by means of the recuperative mechanism shown in Figure 2 of the accompanying drawings. As described above the persorbent material after loading into a series of shell and tube heat exchangers may be exposed to CO2 and subsequently heated. Typically, the temperature of the persorbent prior to exposure may be 273" (units 1-6). Similarly, following the desorption of CO2 the temperature of the remaining persorbent material may be 433°K (units A-F). Thus, by a suitable heat transfer arrangement, exchangers 1-6 may be heated to a temperature approaching 433"K at the expense of the exchangers A-F. For example, consider a heat transfer link between the shell of unit 1 and the shell of unit A employing a conventional heat transfer gas or liquid. On reaching equilibrium (for the sake of mathematical convenience) each unit will have approximately the arithmetic mean temperature of 353"K. Likewise, consider similar links between unit 1 and units B, C, D, E and F. These in turn will give successive equilibrium temperatures for unit 1 of approaching 393°K, 413°K, 423"K, 428"K and 430.5"K. If this process is then repeated for units 2-6, it will be possible to effectively transfer most of the heat of the desorbed material to the freshly sorbed material (probably 95- 98 f < > ) . The connection between the heat exchangers of the same series is thermally poor and includes a suitable valve arrangement for the isolation of each exchanger. Thus, once the cycle has been initiated, it should be possible to maintain the cycle in operation with very little additional heating of the sorbed material or refrigeration of the desorbed material, barring of course other additional isothermal heat input required in stage C-D in Figure 1. Thus, the present Invention also provides a method for transferring heat from material at an initial temperature T 1 held in a number of connected heat exchangers in a first series to material at an initial temperature T held in a number of connected heat exchangers in a second series in which by heat transfer means between each and every one in turn of the exchangers in the said first series with each and every one in turn of the exchangers in the said second series heat may be transferred in discrete stages from the said material at said initial temperature T*. to the said material at said initial temperature T2 so that the final temperature of the said material in the said first series substantially approaches and the final temperature of the said material in the said second series substantially approaches T^. In particular the invention provides a method wherein the said heat transfer means between the said exchangers in each said series are arranged so that each said exchanger in turn and in a first fixed sequence in the said first series reaches an equilibrium temperature successively with each said exchanger in turn and in a second fixed sequence in the said second series thus transferring most of the beat from the said material held in the said first series of exchangers to the said material held in the said second series of exchangers in the said discrete stages. Similarly, the present invention provides apparatus for transferring heat from material at an initial temperature T- ] held in a number of connected heat exchangers in a first series to material at an initial temperature T2 held in a number of connected heat exchangers in a second series comprising heat transfer means between each and every one in turn of the exchangers in the said first series with each and every one in turn of the exchangers in the said second series in order that heat may be transferred in discrete stages from the said material at said Initial temperature T- | to the said material at said initial temperature T so that the final temperature of the said material in the said first series substantially approaches T2 and the final temperature of the said material in the said second series substantially approaches T- j . In particular the Invention provides apparatus wherein the said heat transfer means between the said exchangers in each said series are arranged so that each said exchanger In turn and in a first fixed sequence in the said first series reaches an equilibrium temperature successively with each said exchanger in turn and in a second fixed sequence In the said second series thus transferring most of the heat from the said material held in the said first series of exchangers to the said material held In the said second series of exchangers in the said discrete stages. Other recuperative methods may be employed, e.g. where the heat exchangers are arranged in a continuous circle. By using a sorbent material as described above it is possible (i) to reduce the entropy of the working fluid without cooling, (ii) to increase the temperature of the working fluid at substantially constant volume, and (iil) to desorb the sorbent material isothermally, by providing much of the heat input at the highest cycle temperature during desorption, thus improving cycle efficiency. Figure 3 illustrates a practical self- explanatory flow diagram embodying the present invention based on the temperature/entropy cycle of Figure 1 in combination with the recuperative mechanism of Figure 2, when employing CO2 as a working fluid.

Claims: CLAIMS 1. A method for providing a work performing device with a working fluid having a temperature T" and a pressure P bar in which the said working fluid at a temperature less than T"K and a pressure less than P bar is exposed to a sorbent material (as defined) which is subsequently heated together with the said working fluid at substantially constant volume to give the said working fluid a temperature T"K and a pressure P bar. 2. A method according to Claim 1 wherein the fluid at the temperature T U K and pressure P bar is released to perform work. 3- A method according to Claim 2 wherein the sorbent material is supplied with heat isothermally during desorption at temperature T"K as the pressure decreases from pressure P bar. 4- A method according to Claim 2 or Claim 3 wherein the sorbent material is cooled following the release of said fluid. 5- A method according to Claim 1 wherein the method is cyclically repeated. 6. A method according to Claim 1 wherein the exposure of the sorbent to the working fluid is sustained until a state of substantial equilibrium is reached. 7. A method according to Claim 1 wherein the working fluid comprises a fluid selected from the group consisting of carbon dioxide, water vapour, ammonia, organic hydrocarbons, halogenated hydrocarbons and polyhalogenated hydrocarbons. 8. A method according to Claim 1 wherein said sorbent comprises a sorbent selected from the group consisting of a dehydrated zeolite, and a dehydrated crystalline sodium alumino-silicate. O P1 λ WIPO 9- Apparatus for supplying a work performing device with a fluid at an elevated temperature and pressure, the apparatus comprising a source of fluid, a chamber containing a sorbent for the fluid, heating means for heating the contents of the chamber, and control means, the control means being arranged to supply fluid from the source to the chamber for sorption by the sorbent, to retain the fluid and sorbent in the chamber and to cause the heating means to heat both fluid and sorbent while retained therein, thereby to raise the fluid to an elevated pressure and temperature, and to release the fluid at its elevated temperature and pressure from the chamber and to supply it to the work performing device. 10. Apparatus for supplying fluid at an elevated pressure and temperature to an outlet, the apparatus comprising a plurality of chambers each containing a fluid sorbent material, fluid supply means for supplying fluid to each chamber, heating means for heating the contents of each chamber, and control means for controlling (i) the supply of fluid from the fluid supply means to each chamber, (ii) the supply of fluid from the chamber to the outlet and (iϋ) the heating means, all in such a manner that, each chamber is subject to a plurality of cycles, each cycle including the sequence of supplying fluid from the fluid supply means to the chamber for sorption by the sorbent material therein, heating the chamber and the fluid and sorbent material retained therein whereby to elevate the temperature and pressure of the fluid within the chamber, and releasing the fluid at its elevated temperature and pressure from the chamber to the outlet. 11- Apparatus according to Claim 9 or Claim 10 including means for supplying heat to the sorbent material isother ally during desorption at an elevated temperature as the pressure decreases from an elevated pressure. 12. Apparatus according to Claim 10 including means for cooling each chamber between successive cycles. 13- Apparatus according to Claim 9 or Claim 10 wherein said heating means comprises at least in part an air-conditioning system. 14- Apparatus according to Claim 9 or Claim 10 wherein said sorbent comprises a dehydrated zeolite and said fluid comprises carbon dioxide. 15- A fluid turbine in combination with apparatus according to Claim 9 or Claim 10 wherein the turbine is connected to said outlet to be driven by said fluid at said elevated pressure and temperature. 16. A method for transferring heat from material at an initial temperature T- j held in a number of connected heat exchangers in a first series to material at an Initial temperature T2 held in a number of connected heat exchangers in a second series in which by heat transfer means between each and every one in turn of the exchangers in the said first series with each and every one in turn of the exchangers in the said second series heat may be transferred in discrete stages from the said material at said initial temperature T- j to the said material at said initial temperature T2 so that the final temperature of the said material in the said first series substantially approaches T and the final temperature of the said material in the said second series substantially approaches T- j . 17- A method according to Claim 16 wherein the said heat transfer means between the said exchangers in each said series are arranged so that each said exchanger in turn and in a first fixed sequence in the said first series reaches an equilibrium temperature successively with each said exchanger in turn and in a second fixed sequence in the said second series thus transferring most of the heat from the said material held in the said first series of exchangers to the said material held in the said second series of exchangers in the said discrete stages according to Claim 16. 18. Apparatus for transferring heat from material at an initial temperature T- j held in a number of connected heat exchangers in a first series to material at an initial temperature held in a number of connected heat exchangers in a second series comprising heat transfer means between each and every one in turn of the exchangers in the said first series with each and every one in turn of the exchangers in the said second series in order that heat may be transferred in discrete stages from the said material at said initial temperature T- j to the said material at said initial temperature 2 so that the final temperature of the said material in the said first series substantially approaches T and the final temperature of the said material in the said second series substantially approaches T- | . 19- Apparatus according to Claim 18 wherein the said heat transfer means between the said exchangers in each said series are arranged so that each said exchanger in turn and in a first fixed sequence in the said first series reaches an equilibrium temperature successively with each said exchanger in turn and in a second fixed sequence in the said second series thus transferring most of the heat from OMPl W1PO the said material held in the said first series of exchangers to the said material held in the said second series of exchangers in the said discrete stages according to Claim 18. 20. A method for providing a work performing device with a working fluid substantially as hereinbefore described with reference to Figure 1 or Figure 3 of the accompanying drawings. 21. Apparatus for supplying a work performing device with a fluid substantially as hereinbefore described with reference to Figure 1 or Figure 3 of the accompanying drawings. 22. A method for transferring heat substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings. 23- Apparatus for transferring heat substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

Inventors: RILETT JOHN WALTER, RILETT, JOHN, WALTER
Applicants: RILETT JOHN W, RILETT, JOHN, WALTER
Application year: 1984
Main classification: F01K25
IPC codes: F01K25