GB2094461A - Revaporising liquified gases - Google Patents

Abstract

In hazardous atmospheres it is sometimes necessary to boil off cryogenic liquids and conventional flame heaters cannot then be safely used. Apparatus to overcome this problem includes a diesel engine (18) or a protected electric motor which drives a water brake (20) connected in the hot pass of a heat-exchanger (14), the cold pass of which receives the cryogenic liquid from this source (10). Heat from the engine cooling water may also be circulated through the hot pass (22). Controls (28) ensure that there is no excessive temperature rise and in one modification the engine radiator (30) is fitted with louvres to vary the cooling action. <IMAGE>

Description

SPECIFICATION Apparatus for heating liquids This invention relates to the heating and in particular the boiling of liquids, for example the conversion of cryogenic liquids, such as liquid nitrogen, to gaseous form.

It is common practice, because of the convenience of compactness, to store gases such as nitrogen as cryogenic liquids at temperatures, for example of about --1 96at. The amount of space required is far less than for gaseous storage, but for most applications use of the liquid as such is unsuitable for a number of reasons, and it is, therefore, necessary to reconvert the stored liquid to the gaseous form.

Typically such recoversion is effected by means of a heat-exchanger and a heat source.

Conventional heat sources are based on airblown diesel oil-fired heater systems, but where hazardous environmental conditions exist the use of hot-flame burners is not desirable on safety grounds.

Clearly, one readily available alternative is to use a system with the heat source sited remotely, away from the hazardous area, but such systems then require a transmission system to conduct the heat from the heat source to the heat-exchanger.

To overcome the problems associated with hotflame burners it has already been proposed to make use of a diesel engine driving a hydraulic pump which is subject to a substantial back pressure, so that the oil used in the pump circuit heats up and the heat generated can be transferred in a heat-exchanger to the cryogenic liquid, such as nitrogen, thereby converting the latter to its gaseous form.

Further heat is also available from the engine and exhaust manifold cooling system and this heat is used by incorporating a second heat-exchanger in the system.

This solution to the problem meets safety requirements, but it is very well known that oil is a poor conductor of heat so that the heat-exchanger used must have special characteristics to ensure efficient heat exchange to the cryogenic liquid; furthermore, for optimum effectiveness the hydraulic circuitry should be a pressurized system, typically operating at several thousand Ib./sq. in.

According to the present invention there is provided apparatus for heating a cryogenic liquid comprising supply means for the liquid to be heated, a heat-exchanger through the cold pass of which the cryogenic liquid can be circulated and a power source coupled to a water brake having connections to and from the hot pass of the heatexchanger.

It is commonly recognised that water has outstanding heat transmission properties and the use of a water brake not only allows for exploitation of this fact, but, furthermore, allows for direct coupling to the engine water cooling system without the need for any secondary heatexchanger.

The invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawing, the sole Figure of which is a circuit diagram of apparatus in accordance with the invention.

The apparatus is simple in its overall concept, but nevertheless effective to provide the large quantity of heat necessary to convert a low temperature liquid, such as nitrogen, to its gaseous state. It will be understood that the invention can be applied to other liquids cooled to cryogenic temperatures either for gasifying or merely to raise the liquid temperature. A supply of liquid nitrogen 10 in an insulated tank is delivered either by a pump P, or alternatively by simple pressure decantation to the cold pass 1 2 of a heat-exchanger 14, the outlet of which delivers gaseous nitrogen to the user location 1 6. A diesel engine 1 8, or if desired a specially-protected electric motor is connected to a pressurized water brake 20 of conventional kind, and operable in a closed circuit.The closed circuit includes the hot pass 22 of the heat-exchanger, and it its desirable that this hot pass can, in addition, be connected to the otherwise closed circuit of the engine cooling system 26 and exhaust manifolding, although this is not essential. To avoid undue cooling a thermostat valve 28 is provided so that the radiator 30 can be by-passed.

A conventional engine exhaust gas heatexchanger 26 may also be incorporated into the water system at little extra inconvenience since it will also use water as a heat transfer medium.

A further benefit of the engine exhaust gas heat-exchanger is the resulting cooling, to an acceptable, safe, teperature, of the diesel exhaust gas to atmosphere.

The water brake 20 selected for use is preferably of the kind capable of being incorporated in a closed circuit, such as that marketed by Froude Engineering under the code DPX.

Since the closed circuit will be pressurized it is necessary that the pressure rating of the radiator must be the same as that in the water brake.

While it is preferred that the water brake 20 should operate on a closed circuit principle, it is also possible to use an open circuit water brake the outlet of which is connected to the hot pass of the heat-exchanger. However, pressurization is not, of course, possible with resultant lower efficiencies.

The amount of heat generated in the water brake is substantially directly proportional to the speed of the engine, and the controls necessary to ensure that the temperature of the water is at all times adequate to effect the desired degree of vapourisation are thus linked to a simple engine throttle. Monitoring gauges for pressure and temperature will be incorporated upstream and downstream of the cold pass of the heatexchanger, and similarly for control purposes gauges will be incorporated in the water brake circuit.

As an alternative to the thermostat 28 and bypass, the radiator may be equipped with shutters or louvres disposed adjacent to the radiator core which are controlled by control means which act to keep the temperature in the circuit within desired limits. The louvres are provided with resilient means biasing them to an open position and the control means will keep them closed during normal operation unless there is an excessive temperature rise in which case the resilient means will be allowed to open the louvres.

An advantage of the provision of such louvres is that they give a ready visual indication that the control System is functioning properly.

If the working conditions for the apparatus are particularly hazardous, in place of the diesel engine. a protected electric motor can be used to drive the water brake or, if a convenient compressed air supply is available an air motor can be substituted. The power for the electric motor will, of course, be generated at a position remote from the hazardous atmosphere.

The risk of excess cooling of the hot water from the water brake is avoided by designing the hot pass of the heat-exchanger so that the fiow rate is high. Under such conditions the temperature drop can conveniently be as little as 1 00 F, for example from 16O0Fto 1500F.

As an additional safety precaution in the event that the system should malfunction, it is possible to use in the modification referred to above, an oversize radiator and a thermostatically-controlled engine fan for the diesel engine, the radiator circuit being connected to the hot pass of the heat-exchanger, so that excess heat not removed by the heat-exchanger can be dissipated.

The flow in the, or, each heat-exchanger is preferably contra-flow so as to reduce the very high temperature differential.

The primary heat-exchanger will be dimensioned and generally suitable for accommodating both the cryogenic liquid and the resulting gas.

The liquid pump and the water brake may be on the same shaft as shown in the drawing, or they may be on separate shafts.

A control system can be incorporated to ensure that the output gas is at the required pressure and temperature.

Claims (9)

1. Apparatus for heating a cryogenic liquid comprising supply means for the liquid to be heated, a heat-exchanger through the cold pass of which the cryogenic liquid can be circulated and a power source coupled to a water brake having connections to and from the hot pass of the heatexchanger.

2. Apparatus according to claim 1 , wherein the power-source is a diesel engine and the cooling system thereof is in communication with the hot pass of the heat-exchanger.

3. Apparatus according to claim-2, wherein the hot pass circuit includes a second heat-exchanger forming part of the exhaust manifold of the engine.

4. Apparatus according to claim 1, wherein the power-source is a protected electric motor.

5. Apparatus according to any one of the preceding claims, wherein the heat-exchanger operates with contra-flow.

6. Apparatus according to any one of the preceding claim wherein the cryogenic liquid is pumped to the cold pass of the heat-exchanger and the pump is coupled to the said power-source.

7. Apparatus according to any one of claims 2 to 6 comprising means for varying the degree of cooling of water passing through the radiator of the engine.

8. Apparatus according to claim 7 wherein the means for varying the degree of cooling comprises shutters or louvres disposed adjacent the radiator and thermostatic means operable to vary the degree of opening of the louvres.

9. Apparatua for heating a liquid substantially as hereinbefore described with reference to the accompanying drawing.