Metal hydride compressor control device and method

Abstract

The present relates to a Metal hydride compressor control method for generating a variable output pressure P.sub._desired_outPut, comprising a first step of inflowing gaseous hydrogen into a metal hydride compartment at a constant temperature and then stopping the gaseous hydrogen inflow, a second step of heating the metal hydride to a predetermined temperature which corresponds to a temperature which passes through the α+β phase at the desired output pressure P.sub._desired_output, a third step of opening the output connection of the compressor and keeping it at a constant pressure by regulating the temperature to keep a constant output pressure P.sub._desired_outPut until the system completely leaves the α+β phase.

Claims

1. Metal hydride compressor control method for generating a variable output pressure P.sub._desired_output, comprising a first step of inflowing gaseous hydrogen into a metal hydride compartment at a constant temperature and then stopping the gaseous hydrogen inflow, a second step of heating the metal hydride to a predetermined temperature, which corresponds to a temperature, which passes through an α+β phase and leaves the α+β phase at the desired output pressure P.sub._desired_output a third step of opening an output connection of the compressor and keeping it at a constant pressure by regulating the temperature to keep a constant output pressure P.sub._desired_output until the system completely leaves the α+β phase.

2. Metal hydride compressor control method according to claim 1, characterized in that the first step also comprises cooling the metal hydride to keep its temperature constant.

3. Metal hydride compressor control method to claim 1 characterized in that the first step is continued until the border of the α+β phase is reached.

4. Metal hydride compressor control method according to claim 1 characterized in that the temperature regulation is done with a control approach chosen in the group including PID control, MIMO control or control with any number of inputs and outputs and different sensing devices.

5. Metal hydride compressor control method according to claim 1 to characterized in that a connection to a gaseous hydrogen source is closed using a closing means.

6. Metal hydride compressor control method according to claim 1 characterized in that the output connection of the compressor is opened with a opening/closing means.

7. Metal hydride compressor control method according to claim 1 characterized in that at the end of step three, when the H.sub.2 has been completely outputted, the output connection is closed and the system is cooled down.

8. Metal hydride compressor control method according to claim 1 characterized in that at the end of the cooling a further cycle starts again, to generate a different pressure than in the previous cycle by choosing a different temperature T3 in the second step.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further particular advantages and features of the invention will become more apparent from the following non-limitative description of at least one embodiment of the invention which will refer to the accompanying drawings, wherein

(2) FIG. 1 represents a pressure-composition isothermal curve with Van't Hoff plot of the method of the present invention,

DETAILED DESCRIPTION OF THE INVENTION

(3) The present detailed description is intended to illustrate the invention in a non-limitative manner since any feature of an embodiment may be combined with any other feature of a different embodiment in an advantageous manner.

(4) The present invention relates to a single or multi-stage metal hydride compressor control method where the compression ratio is not fixed but can be varied or adjusted by a user.

(5) More specifically, the hydrogen outflow pressure is regulated to the required level in some range of values by controlling the temperature with the method of the present invention. The single or multi-stage metal hydride compressor control method comprises a first step of inflowing gaseous hydrogen into a metal hydride compartment at a constant temperature T1=T2 while cooling the metal hydride the cooling method can be passive, e.g. by ambient convection, or active, e.g. via some liquid cooling path or forced, air convection. In FIG. 1, this step is represented by the state moving from point 1 along the isothermal until the border of the α+β phase is reached in point 2.

(6) The temperature is monitored using for example a thermocouple or an RTD and the pressure is monitored using a conventional pressure sensor. Once point T2 is reached, the gaseous hydrogen inflow is stopped and the connection to the gaseous hydrogen source is closed using some closing means, e.g. a mechanical or electrical valve or any other closing mean.

(7) At this point, in a second step, the metal hydride is heated to some pre-calculated or online-calculated temperature T3 at point 3 of FIG. 1, which corresponds to the temperature, which passes through the α+β phase at the desired output pressure P.sub._desired_output. In FIG. 3, this is represented by the vertical line joining point 2 to point 3. The temperature T3 depends on various parameters but the most significant ones are the material used and the desired output pressure P.sub._desired_output.

(8) Once the desired output pressure P.sub._desired_output is reached due to heating to T3, the output connection of the compressor is opened with some opening/closing means, e.g. a valve or any other electrical, mechanical or electromechanical system and the system is kept at a constant pressure by regulating the temperature. As a matter of fact, since the desorption reaction is endothermic, additional heat has to be provided to the system in order to maintain the pressure constant.

(9) This regulation can be done with any control approach including Proportional, Integral, and derivative (PID) control, Multiple Inputs, Multiple Outputs (MIMO) control or control with any number of inputs and outputs and different sensing devices, most notably including one or several temperature and pressure sensing devices.

(10) The system then moves along the isothermal from point 3 and at some point, it will again enter the α+β phase.

(11) The system is then kept at the right temperature to guarantee a constant output pressure P.sub._desired_output until it leaves the α+β phase at point 4.

(12) When the latter step is finished, i.e. when the H.sub.2 has been completely outputted, the output connection is closed and the system is cooled down to point 1 where the cycle starts again, possibly to generate a different pressure than in the previous cycle by choosing a different temperature T3 in step 2.

(13) Another aspect of this invention relates to a single or multi-stage metal hydride compressor in which the above method is carried out. Such single or multi-stage metal hydride compressor has a variable output pressure P.sub._desired_output which is kept constant (or variable according to some determined function of time) using temperature control in one or multiple areas of the device.

(14) According to preferred embodiment, the metal hydride compressor is a multi-stage metal hydride where each stage comprises a different material and receives a desired P.sub._desired_output as an input from the preceding stage.

(15) Such a compressor can be used in applications where variable compression ratios are needed which include but is not limited to compressors for use in laboratories that provide compressed and/or purified hydrogen for experiments, compressors for use in industrial hydrogen compression applications, compressors for use in hydrogen gas stations and compressors for the use in hydrogen or metal hydride energy storage systems comprising fuel cells and/or electrolyzers.

(16) While the embodiments have been described in conjunction with a number of embodiments, it is evident that many alternatives, modifications and variations would be or are apparent to those of ordinary skill in the applicable arts. Accordingly, this disclosure is intended to embrace all such alternatives, modifications, equivalents and variations that are within the scope of this disclosure. This for example is particularly the case regarding the exact temperature used, the material used, the monitoring system, the number of stages, the temperature sensor and all the different apparatuses, which can be used in conjunction with the present invention.