Thermochemical Energy Storage and Mechanical Energy Converter System

The present invention generally relates to an energy supply and more particularly to a power system using energy in chemical form. The supply can be held in readiness for extended periods of time without energy loss.

This is a distinct advantage over thermal energy storage systems that rely on insulation to retain stored energy. An advantage of the present system over an electric storage battery is that only heat is required to recharge the system rather than less readily available electric power.

It is therefore a general object of the present invention to provide an improved power system. The system operates in a Z-cycle and comprises an intermittent operating thermochemical mechanical energy converter. In the power phase heat is added to an ammoniate CaCl.sub.2.8NH.sub.3 and forms an ammoniated salt CaCl.sub.2.2NH.sub.3 with the release of ammonia gas that does work by isentropic expansion through an engine. The ammonia forms a second ammoniate ZnCl.sub.2.2NH.sub.3 with the release of heat that is returned to the ammoniate CaCl.sub.2.8NH.sub.3 to keep the process going. During the reactivation phase heat is added to ZnCl.sub.2.2NH.sub.3 and releases ammonia gas to the CaCl.sub.2.2NH.sub.3 so that the power phase can be restarted.

FIG. 1 is a pressure vs. temperature plot showing the Z-cycle in which the present invention operates;

FIG. 2 is a schematic diagram of a system for performing the power phase in accordance with the present invention;

FIG. 3 is a schematic diagram of a system for performing the reactivation phase in accordance with the present invention; and

FIG. 4 is a schematic diagram of the complete system in accordance with the present invention.

Referring now to FIG. 1 there is shown a Z-cycle in which the present system operates. In the operation of the Z-cycle energy is stored in chemical form by means of an ammoniated salt. When ammonia is added to the salt to form an ammoniate, heat is released. Conversely, the addition of heat to the ammoniate frees ammonia gas. When this is done at high pressure and temperature, and the gas superheated, the gas can be isentropically expanded through an engine or turbine to produce work. When the exhaust is added to another salt, another ammoniate is formed with the release of heat. In our case the heat released by ammoniation of the second salt is sufficient to deammoniate the first ammoniate and superheat both the intake gas to the turbine and the exhaust gas from the turbine.

The process at state A, in FIG. 1, is for example:

and at state B:

For the equation (1) and (2) processes the Clausius-Clapeyron Equation holds; the slope of the lines is

where R=universal gas constant

In the cycle A-B-C-A-D work is produced during isentropic expansion from state C to state A. State B to state C and state A to state D are constant pressure superheating processes. State A to state B is essentially a heating process at constant volume. T.sub.C .ltoreq.T.sub.D. When all of the ZnCl.sub.2 is ammoniated to ZnCl.sub.2.2NH.sub.3 or when all the CaCl.sub.2.8NH.sub.3 is deammoniated to CaCl.sub.2.2NH.sub.3 the process ceases. The CaCl.sub.2 is in the lower ammoniate state, CaCl.sub.2.2NH.sub.3. To re-energize the system, heat is added at a temperature greater than T.sub.D to the ZnCl.sub.2.2NH.sub.3 driving off all of the ammonia gas NH.sub.3. The ammonia gas NH.sub.3 flows from state D to state A where the higher ammoniate CaCl.sub.2.8NH.sub.3 is formed. Heat is released at temperature T.sub.A and is rejected to the environment, which must be a lower temperature. The process is now ready to be repeated.

Refer now to FIG. 2 for a system shown schematically that performs the power phase. The system comprises a first reactor 10 containing ammoniate CaCl.sub.2.8NH.sub.3 and a second reactor 12 containing zinc chloride ZnCl.sub.2. The first and second reactors are connected to each other by the serial combination of piping 16 and 18, valve 20, and turbine 22. The turbine 22 drives a propeller 24.

When valve 20 is opened ammonia gas NH.sub.3 flows through piping 16 to turbine 22 where work is produced such as driving the propeller 24. The turbine exhaust gas passes through piping 18 to reactor 12 where the gas combines with the ZnCl.sub.2 to produce ZnCl.sub.2.2NH.sub.3 and release heat at a high temperature. This heat is transferred by a heat transfer loop to the CaCl.sub.2.8NH.sub.3 driving off more NH.sub.3 to drive the turbine. The initial pressure in the CaCl.sub.2 reactor 10 must be slightly greater than in the ZnCl.sub.2 reactor 12 for this bootstrap system to get started.

The process continues until all the CaCl.sub.2.8NH.sub.3 has been deammoniated to CaCl.sub.2.2NH.sub.3 or all the ZnCl.sub.2 has been ammoniated to ZnCl.sub.2.2NH.sub.3 or both. During the period both reactors are well insulated.

To reactivate or re-energize the system, it is connected as shown in FIG. 3. Heat is added to the reactor 12 containing the ZnCl.sub.2.2NH.sub.3. The ZnCl.sub.2 is deammoniated and released ammonia gas flows through piping 18 and 16, and opens valve 28 to reactor 10. This produces CaCl.sub.2.8NH.sub.3 and releases heat which is rejected to the environment.

The processes of power production and reactivation can be carried out in the total system shown in FIG. 4. The system comprising reactors 10 and 12 connected through piping 16 and 18, valves 20 and 28, and the turbine 22 driving propeller 24. The heat transfer loop 26 has a valve 30 and a circulating pump 32. A heat exchanger 34 receives a source of cooling water through valve 36 for reactor 10. A heat exchanger 38 receives a source of hot water or other hot fluid through valve 40.

In operation during the power phase, valves 20 and 30 are open, valves 28, 36 and 40 are closed, and circulating pump 32 is operating. During the reactivation phase valves 20 and 30 are closed, valves 28, 36 and 40 are open, and circulating pump 32 is shutdown.

In operation during the power phase is similar to that described in FIG. 2 with ammonia gas NH.sub.3 flowing from reactor 10 to reactor 12 with work being done by turbine 22. The ammonia gas produces ZnCl.sub.2.2NH.sub.3 in reactor 12 and releases heat. The heat is transferred back to reactor 10 by the operation of circulating pump 32 in heat transfer loop 28.

Upon completion of the power phase, the reactivation phase lineup of valves is made and the reactivation phase is started. The operation of the reactivation phase is similar to that described in FIG. 3 with ammonia gas flowing from reactor 12 to reactor 10 through valve 28. Heat is added to reactor 12 by heat exchanger 38 and heat is rejected to the atmosphere by heat exchanger 34 following the release of heat from the production of CaCl.sub.2.8NH.sub.3 in reactor 10.

There has therefore been described a thermochemical energy storage and mechanical energy converter system utilizing both a power and a charge phase. The charge phase enables the reuse of the system once the original working fluid has been spent.

It will be understood that various changes in details, materials, steps and arrangement of parts, which have been described may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.